I witnessed a white 97-ish Z-28 with nuthin' but a Borla cat back system kick some major butt out at the Martin Sports Car club autocross in Orlando a couple of years ago. I have some video of it somewhere.
A NSX owner I spoke to, said the Z-28 driver was beating his NSX's times in a big way.
The Z-28 driver also knew what he was doing on the track.

In capable hands a V8 rear drive car is probably one of the best autocross vehicles. It's hard to drive fast, but if you can do it, you would be hard to catch.
Front driver vehicles have their inherent auto-x issues too. Understeer mostly. Also, when your turning wheels and driving wheels are one in the same, the results can be less than pleasing.

I remember an article recently in some import mag where they tested a stock Mustang GT against a Type-R on a race track. The GT walked all over the R by two seconds a lap!!!! And both cars were driven by import guys. I was suprised they even admitted the mustang's triumph in the article.