With stock suspension and relatively soft sidewall tires like the Goodyears, you'll want to keep them pretty high. With more camber, rear roll stiffness, and total roll stiffness you can soften them up a bit, but it's hard to keep the tires from rolling over on a stock car. You proabably will find there's not much difference between 40 and 5 psi in terms of speed, but I'd guess wear will be best more towards 50 (cold) psi. I have run 48 psi with good luck, on stock suspension. Around 30 seems to be good in the rear, depending on the tire. I needed 34-36 to keep the Fusions from going too mushy in the back, but the MXs feel great at 30 psi.
