Stock Vs Stock
300zx twin turbo and 370z perform the best on paper.
First gens, also known as S30s, are the best candidate to modify for many racing applications, as they are the lightest, and were more of a dedicated race car when produced, than the later, more luxurious models.
280zx's (1979-1983) have a much better steering angle than the earlier z cars though, and can truly phenominal race cars, as seen by Barb Sharp's 650hp L28et powered 280zx that was very successful racing in the 80's.