Have to say that I really like how the Fugu drives with
@Mistah_MCA's setup. Felt really composed while having plenty of top-end grunt for the straights and slipstream trains, and a lot better than the setup I tried to make from scratch in my initial FP trial.
So, to start today's proceedings off, I decided to give Nations a try to see if I could get the most out of his settings...
(Be warned, this is a very,
very long post!)
14:00 Nations
First attempt was the 14:00, also featuring
@T_revisio. Got stuck behind traffic on my first flyer (2:20.840), and had to abort my second when the Frenchman in front of me smacked the wall under the bridge. Problem was that while I had clean air, I was too far behind the pack of cars ahead to get a good slipstream. Thus, while I managed to improve my initial time with a 2:20.724, it was only good enough for 18th -
2.9 seconds off the polesitter!
Had a fairly decent first couple of laps, jumping to 14th while avoiding scraps, making a nice move on a German driver and taking advantage of others' penalties. German fought back by steamrolling his way up the inside of the final right-hander, but for a while was still in a good place and got into some fairly close battles. All progress undone by several wall collisions - the biggest earning me a 1.5-second penalty - eventually leading to me dropping to 19th and last by the final lap. Lost so much time at that point that I decided it wasn't worth fighting back and did a doughnut before the pit straight.
And I tell you now, I was kicking after that one. Mistah_MCA's wonderful setup squandered by traffic, lack of slipstream in qualifying and my own carelessness.
15:20 Manufacturers
Of course, Manufacturers remained my primary focus, but I went into the 15:20 rather unhappy with how the Mustang had felt in test lobbies. Indeed, I initially considered not joining at all after the disastrous 14:00 run, but eventually pressed on just to see if things would turn out differently.
@Lost Sheltie, T_revisio and my French teammate were present, but sadly there was to be no improvement. Was forced to abort my planned first lap after a yellow and blue BMW cut across my front bumper through Turn 15. There was contact; I turned below the white line and immediately returned to the lobby for a fresh run. Set a 1:40.050 followed by a tyre change and a 1:39.288, which left me starting 20th and last. The only consolation was that the gap between myself and the pole-sitting Mazda was just under 1.2 seconds, but this didn't help my already crestfallen mood.
Race started a bit better, though. Fought past a McLaren, Toyota and Lexus to get up to 17th by the end of Lap 2, but the Lexus wasn't having any of it, repeatedly trying to push and nudge his way back after an early penalty. Things came to a head on Lap 6 when I tried to line up a pass on the red GT-R going into Turn 8; the Lexus punts me forward, I end up clouting the GT-R into a half-spin before the pinball effect repeats the process again. Lost my entire momentum at that point, though the Toyota's lack of straight-line speed enabled the Mustang to get it easily down the pit straight.
Caught up with the bottom pack again, only to be collected by the GT-R as he runs wide and loses it at Mergulho. Thankfully I come through the incident fairly intact, but as I look back I notice that he has picked up a 2-second penalty purely for hitting my passenger-side door. Seeing that he was still at Juncao by the time I was approaching the line, I thought it was unfair to leave the GT-R behind, and that he was penalised for what was essentially a racing incident when the Lexus ruined both of our races without as much of a raised eyebrow. So, I pulled off at the Senna curves until the GT-R had passed, and chose to remain behind him to the flag. At some point, another GT-R left the race upon receiving a track limits penalty, putting us up to 18th and 19th respectively.
Have to say that the Mustang felt decent up until the incidents started occurring, but it was another case where my qualifying left a lot to be desired. My teammate's 10th-place finish proves that the Mustang can work well around Interlagos, but for whatever reason I just couldn't get a good feel at the time.
16:40 Nations
The outcome of the first two lobbies, while infuriating, gave me the motivation to try both rounds again. Probably because of the DR drop I had incurred, qualifying for the 16:40 was more promising. Four consistent mid-2:20s in slipstream and traffic, the best being a 2:20.403 set early into the session. Good enough for 9th on the grid right in front of T_revisio.
Thought there was a chance I could fight my way through the top-10, but started hitting the walls too often and had to give up two spots on the first lap - one to T_revisio, the other to a green German driver who as it turned out seemed hostile to the idea of me slipstreaming my way past. Watched him push a Swiss driver wide through the final turn, allowing me to retake 10th; then, the longer gearing of Mistah_MCA's tune gave me the legs to slipstream around the outside of the German into Turn 1.
Something I didn't realise until later was that the Swiss Fugu tapped the German as I tried to keep myself steady around the outside. What happens next is that the German ends up squeezing me into the wall... and
I get a 1-second penalty for it! 
In hindsight, this wasn't entirely the German's fault, but the very next lap he weaves across the straight trying to break the slipstream. I get round the outside like before; he in turn gets a bit of slipstream but I try and force him to go to the outside. Under braking he moves to the inside, slides and forces me into the wall
again. I was aware that he was planning to pass anyway, so kept as far to the outside as possible, but apparently this wasn't enough to stop the contact and
a second 1-second penalty being served my way.

Another experience of the system being out of order, but there you go. A lonely and still sloppy run to 11th followed.
To add further insult to injury, it was while looking through the lobby screen after the race that I learnt that the penalties amounted to a red SR 'S'.

But still, a better run and a better points score. I was tempted to try the 19:20 slot, but decided against it as I'd rather hang on to 164 points than risk losing them through an even poorer finish.
20:40 Manufacturers
Last slot of the day turned out to be the best. Had the luxury of two Mustang teammates alongside Belgian 'wifi password' and was initially content with the 1:38.773 I set early into qualifying. But again, it couldn't translate into a decent grid slot, and a few issues - including being out of slipstream and one moment where my controller suddenly disconnected while coming out of Pinheirinho. Needless to say, that lap was the fastest I could get, which was still a respectable six-tenths off the South African GT-R on pole. Started 13th with my teammates in 9th and 14th. Had to feel sorry for 'wifipassword' starting dead last in the Alfa.
Initially followed a yellow Mercedes in a train led by the French Mustang. Things kicked off when a MYTEAM Ferrari went wide at both parts of the Senna curves while trying to pass a yellow Subaru; this allowed me and my Swiss teammate to pass him from both sides from Reta Oposta to Descida do Lago. On Lap 5, the Mercedes overshoots the Senna curves and rejoins right alongside the Mazda following behind me. Was incredibly lucky to avoid getting collected, and spent a good few laps pressuring said Honda for 11th. Towards the end, the same Subaru that was forced wide by the Ferrari earlier goes wide a second time, allowing us to catch up and form a frantic five-car battle. A Danish Citroen was making up ground along with the Ferrari, but I hung on as the Subaru picked up penalties and the Honda went wide at Descida do Lago.
Up into 10th I went, but the Honda fights back, running side-by side with me after the Mustang runs a little too wide out of Turn 7. Held off the Citroen with a good exit from Bico do Pato, then watched as the Honda slid under braking at Juncao. Squeezed back into 10th while just about avoiding contact, but not for long as the Citroen
and Ferrari dive up the inside of the first Senna curve. At this point we were going three-wide through the complex, and ultimately I chose to give way so all four of us could survive in one piece (the Subaru, meanwhile, had gone off to Narnia and would go on to ruin a Scirocco's race). Surviving in one piece, as it would turn out, was easier said than done...
Under braking for Descida do Lago, I notice the Honda suddenly surge forwards in my rear-view mirror. Squealing tyres, a faint thud; what's going on? Turns out that he was completely unsighted to the Ferrari braking early ahead of him and had ducked to the infield grass to avoid him. Stayed wide as the Ferrari slowed down in unison, out of expectation that a pass was incoming… and watched as the Honda took the Citroen out on the apex. Just like that, we're back in 11th, and follow the Ferrari home without any further incident. Teammates finished 5th and 9th.
Won't lie in saying that these were among the most frustrating and confidence-knocking FIA races I've had this year. SR restored, thank goodness, but nearly 2,900 DR points lost through a mix of misfortune, wall scrapes, contact, penalties and me just not being fast enough when it counted. There were hopes of fighting from the back and challenging for top 10 positions, and at least Mistah_MCA's tune worked really well, but all the same I can only apologise to Mistah_MCA himself for not making the most of it. Really tough afternoon, but hopefully it won't be too long before I can bounce back.