It may be surprising buy many auto cross guys recommend runnng HIGHER psi for the track than on the street. It may be due to the extreme sidewall pressures the tires have to endure in the hard cornering.
In a typical auto cross you will be using 2nd gear only, no shifting, speeds around 60-65 mph max, or less. No way you will use or need 500 horse, but no one else will either.
I ran with a couple of FFR's, street cars BUT, extremely well setup specifically for auto cross. For race day they were prepped and then trailered to the track, not driven. One car was dry sumped, both had IRS, experienced drivers, racing seats, etc. etc.
They were among the top competitors, almost as fast a some VERY exotic full blown race cars. Like the Lotus 7 replica with a small block V8 and massive slicks. The FFR's were real close to HIS time and he was the fastest of the day.
I was considerably slower, even with full race only Goodyear slicks. The dual carbs are a serious problem for me though, side pivot floats don't do well in hard cornering. You go rich on one corner and lean on the next.
Because your only using one gear (like 2nd) I use my left foot for brakeing. Our auto cross here is NOT typical, it's actually a real track and is faster than a cone setup type track. 75 to 80 mph in some parts, really winds the motor up high, but no time to shift, but some guys do anyway.