Regarding the ZR1. You could remove the turbo or engine upgrades from the list. Because they are easy to spot on replays. This is to keep the tourqe numbers down. I totally agree that the car got to much tourqe on the low rpm's.. Shifts won't be as important. On the other hand, you would'nt need to shift that often in a stock ZR1 either for that matter, nor the ACR Viper. A lot of american supercars use a lot of volume to keep maintanance and durability at decent levels. On the other hand, you got the 458 Ferrari with 560 hp from a 4,5 liter engine. To get that amout of hp from such a small engine you need the engine to be able to rew extremely high (for a road going car). As we all know: tourqe * revs = power, POWER is what moves your car. To get a lot of power from an engine with low rpm's, you need tourqe. So in other words, the bigger the volume the less important the gearchoice gets. Compare this with an F1 engine in the middle of the 90's that produced around 800-850 hp from a 3,5 liter engine.. How is this possible?? To get that amout of HP (power) from a 3,5 liter engine you need to make it rev high.. I think the revlimiter on the mid 90's F1's was around 19-20000 rpm's. And on a side note, the tourqe from this F1 engine was not greater than 300 Nm, which is about the same as you get from your everyday car. On the otyher hand, you got the american supercars ZR1 and ACR with a 6,2 l engine producing 638 hp with the help of a compressor and for the ACR a 8,4 l engine that produces 600 hp. If you compare the HP/l you can clearly see what an achievment ferrari did.
Ferrari 458: 560/4,5=125 hp/liter
Corvette ZR1: 638/6,2=103 hp/liter (with a compressor)
Viper ACR: 600/8,4=71hp/liter
To create an engine that produces more than 100hp/liter without a turbo or supercharger is a real achievment. An example, the BMW M3 E46 produces 343 hp from a 3,4 liter engine. making the hp/l end up at 100,8. Or the E60 M5 with a 5 l engine producing 507 hp ends up at 101,4. When looking at these numbers, Ferrari has done an exeptional achievment with the 458. On the down side, the owner need to spend huge amounts of money on maintainance.
I really like cars with less tourqe and more revs. I think they are much more fun to drive. With this said, I'd suggest you remove all upgrades that can be policed and see if you coud get the tourqe numbers down.
And regarding the choice of tyres. S3 is (if you compare the skid pad tests) almost race tyre performance. S2 would simulate something like TOYO888's or Michelin PILOT SPORT CUP which are road leagal slicks. The S1's would be more like the most expensive high performance road tyre. Something like the Bridgestone POTENZA or Michelin PILOT SPORT II. But since GT5 does not calculate tyre with when grip is calculated, the choice of tyre could for a car like the ZR1 jump up a step on the latter. If a ZR1 is delivered from the factory with something similar to S1's, the with of the tyres (which is not calculated in GT5) could make the realistic choice in GT5 be an S2 tyre. If you add that we tune the car, I'd say that the S3 is perfect. 👍
Oh, my god... Wall of post.
).
with 680hp). 
Personally I prefer the S3's for a number of reasons, but I will say the durability of them sucks once you start putting them on such cars like the Round 1 ZR1, which has a ton of power and relatively little DF. It's too bad there's not a tire between a S3 and R1...because IMO that would be perfect. Anyway, If people are finding the first round to be just too damn difficult in testing, we may end up switching to R1's (just for this round) to try and get everyone on a bit more of a even playing field in terms of pace.
At the end of the day I really want to promote some good racing most importantly...not just a test to find out who the best driver is with little racing involved or and an excercise which is too dependent on tire management skills.
But when you get down to it hp per liter is rather meaningless in the whole scheme of things, when it comes to outright performance. For example, the LS7 in the C6 Z06 might be 7.0 liters and produce 500hp (very mildly tuned from the factory), but it is really similar in phsyical dimension and weight to the 4.5 liter V8 found in the Ferrari or the 4.0 S65 V8 in the newest M3...due to the fact the LS7 is pushrod layout and doesn't have the added weight and complexity that comes along with a DOHC arrangement. Also, the tractability/powerband is extremely useable with the LS7 and the fuel economy is just as good if not better with the LS7 than the smaller DOHC V8's. Of course maintnance cost and modifying cost are also much cheaper as you know. Also you can get 650rwhp (~750hp) normally aspirated out of the LS7 on pump gas with heads/cams and full bolt ons...which is incredible impressive for a motor of it's size and weight. That would impossible to achieve with the Ferrari or BMW motor in normally aspirated form (on 91 octane at least) which are of basically the same physical dimension and weight of the LS7. 
