I've seen both premiums and standard cars warp, but I think it's more due to connection issues than the computational limitations of the PS3.
I agree with everyone: downforce is not currently a major player in the outcome of the race (I won the last race without any wings, and the DN-Xs poor performance could actually have been a by-product of its aerodynamic additions). Plus I think the wings still add drag and would cause extra fuel use and might limit the speeds of cars that use them.
The rally cars are also, perhaps, a bit more of a double-edged sword than they look at first glance. I believe they are all 2L Turbos, which puts a limit on their top-end power and makes them drink fuel fast. I'm not sure if their better handling would put them far enough ahead to make up for fuel use. But they are the only full "race" cars which meet the requirements, however, they are at least the same chassis and body panels as their stock cousins (unlike most other race cars).
The regulations set for the first race are really good. The weight is high enough that only street cars can enter, but not so high it allows only 4WD. The power requirements allow for probably 100 cars to choose from with varying degrees of viability and I'm pretty sure there are at least 16 good choices for competitors (I know of at least the later generation WRC cars, DN-X, RGT, Esprit, M3 GTR Road Car, Z4M, Evora, 370Z, Civic Type R, S2000, STis, Evos, RX-7, Amimaya RX-7, 512BB, R32 through R34 GT-R, Mustangs, NSX Type R, Renault Avantime (for the brave few), and quite a few more). I would like the power regs raised one notch, but that's just me wanting to add a better exhaust to my Porsche (and maybe to allow the R8 into the grid)