Fellow DS3 user here,
TC and SRF off
Analog sticks for controls
Agreed that a good tune especially LSD, Camber and Toe settings help getting the power down!
The other thing I try and do is keep the use of the power limiter to a minimum, why add the stage 3 turbo and all the extra down force you can - to just pull back further on the PL% - and then comment its too easy..
Quick question;
Do AI cars get different gear ratios and down force settings for differing tracks?
Or do they always run the same settings?
They always run the default gear ratios, and I'm certain (though without proof) that they use stock aero and suspension settings as well. They do sometimes upgrade street cars as some of them have much more power than stock, but I highly doubt that whatever parts they add are set to anything but default values.
There's actually at least one race (the first one with proper GT cars in it) where a number of cars are dramatically de-tuned somehow. I'm not sure how they accomplish this as it was like that even before the power limiter was added. It rather annoyed me as I saw the Camaro LM was in the race so I waited to do it until I could get my hands on one, only to find out that the one the AI drove had half the power mine did.
But the gears for sure are always default. If you set your transmission up in a one-make event like the FGT races, you can easily tell your car from the others in the pre-race screens when it goes by on the fast straights as it is the only one that is in the right rpm range, while the others are all revving way too low or bouncing off the limiter. They always hit the limiter (if they can) at the same speed on every track as well, if you watch them when you are racing them.
EDIT: Triggers for gas/brake, X and square for shifting here... when I am using DS3. I was reluctant to switch to triggers at first but after playing enough games that forced me to use them I got used to it.
Throttle response on the DS3 is not linear which makes controlling it very difficult without a lot of practice. Some people say it is better on the analog stick, but I found it to react the same uneven way as it does with the trigger, so I switched back to L2/R2 for easier access to the brake. It might seem a little unusual at first, but some people use the stick for gas and a trigger for the brake, which lets you use both if you need to while still having the old standard stick-throttle.
Brake response is perfectly linear and so braking even without ABS is no problem on the DS3 with only a little practice. Since I use my wheel most of the time, I have a lot of trouble adjusting to the odd throttle and steering, but two or three hard braking maneuvers and that comes right back.