cbramey,
The S2000 is certainly faster than most, perhaps all, of these cars in stock-class form, but this isn't stock class. The tire-width and wheel-width limitations (255 mm and 9 inches) are there to level the playing field between larger, more powerful cars and smaller, less powerful cars. Those limits favor lighter cars.
There was recently a good article in GRM where the author numerically compared the cars eligible for the class. He concluded that the S2k and NC Miata will likely be the strongest contenders, but that the MR-S and early NB Miatas could also do well.
Since I'll only be competing locally, I'm glad to campaign my NC, since I like that car for other reasons.
As for your question about the C4 'Vette, I can't say.
Autocross: STR #13 2009 Miata.
HPDE: #144 1995 Miata.
For sale: 2004 Mazadaspeed Miata.