i bought a C5Z because it out performs the C6 in 1/4 mile and the road corse. its cheeper and with the money you save over the C6 you can mod it and still be faster, close to a C6Z in fact if not faster. if you want you can take mine for a drive, yes its an 01' but with the mods already done i have the same power output that a stock 02-04 has if not a little more.
what are you wanting to do with the car? race it? C5Z>C6. just drive around C6>C5Z.
there are huge differences, the transmission in the C5Z had different ratios than the C6. the brakes have no real feel to them on the C6 and there is next to no steering feedback. the car handles better and the interior doesn't look as cheep on the C5.
read corvetteforum.com and alot of people are selling there C6 to get back into a C5Z.
let me know if you want a ride, we can get together when its not raining or snowing.
i have worked on and driven alot of C5 and C6 vettes and i am glad i went with the C5.