[See5]

CT4BW seems to be the best in-between option if you're considering those two IMO.

Has an extremely accomplished chassis and you can probably swing a killer deal from Cadillac at this point. It'll make an easy 475-500whp with just a tune if you're so inclined.

I had an S550 Mustang Bullitt with full FP suspension, 285/295 tire setup, Mach 1/PP2 shock tune, and front/rear subframe braces(basically equivalent to a GT350) and while very good, probably was still a little behind the Alpha platform cars in terms of balance and chassis integration.

In terms of a non-purpose built sportscar platform, the Alpha cars are probably at the top of the list to me.