My wrx is stage2 + protune and other small goodies and only dyno'd 240whp. I don't go around spanking C5's or anything, but I have put a car on a C5 a couple of times (different occasions). My car will match their 1/4 mile times and I have more aggressive lower gearing.
I wouldn't even bother trying to race from a roll or a modded C5 or Z06 from anywhere though. Stage2+ wrx's shouldn't expect to win from a dig, but just the same they shouldn't be afraid either (if the vette is stock).