I´ve made a test on Deep Forest, which is a track that I know pretty well. I drove each car for 10 laps, and used the same settings. All AIDS off, ABS 1. Tires were Racing Soft.
Results:
1:Nissan Nismo Z (Stock 534hp).......................1´07.486
2:Honda Raybrig (Stage 3 Turbo,no oil c. 530hp) 1´07.708 +0.222
3:Nissan YH GT-R(Stock 518hp)........................1´07.722 +0.236
4:Toyta YH Supra(oil c.+eng.stage 3, 534hp).......1´07.856 +0.370
5:Lexus Tom´s P (oil c.+stage 2 Turbo, 525hp)....1´07.995 +0.509
6:Lexus Tom´s P (Stock, oil c. 490hp)................1´08.880 +1.394
As You can see from the results, the Nismo Z was the fastest even if the others were modified (except the GT-R). Think the gaps would even be bigger if all was stock.
I´m not a "Pro Driver" like the most of You, but I like to do these kind of tests and compare cars.
In my opinion the Nissan got the best brakes, Honda has the best topspeed but is very slippery, Toyota has probably the worst brakes, Lexus is fun to drive but even with 525 hp it was last in the test.Stock it is almost 1.5 sec behind on a short track like Deep Forest.
About the Q-session goin online offcourse eliminates people using SRF, but without the data log from the replays it would be impossible to say if someone´s cheating with turbos or engine stages, specially in the GT300 class. But that´s barely not something to be worried about...?