I also own both cars and I think they both have their strongpoints, with the overall winner being the GT hands down for total car, performance, curb appeal and driving feel all combined. However as a pure track car I lean to the Z06 as it is a little faster in stock form as my timeslips can verify! Actually it is the fastest pure stock car I have ever driven, and now new ones can be bought in the mid 60's price range, make it truly the best bargain I have ever seen for an economy supercar that looks damn good as well IMO.
When you say timeslips, are referring to 1/4 mile?. What did you run in the Z?. I have a C5Z and do drag nights and some closed track with a friend with an 07.
I have driven all three pretty hard. The C6 is such a huge upgrade as a driver than the C5. It feels lighter on it's feet and both steering and brakes are better, as is road noise. It's real hard to find fault with the C6. But when you compare to the GT I think the GT is another notch above in pure chassis refinement. The C6 is still surprisingly good with the same old leaf spring platform.
The GT does not give you the sense of speed that you get from the Z. So it makes the GT feel slower without all the engine noise up front and through the cabin. We did several roll on tests at a motorsports facility. The gearing for the Z I like better that the GT. Depending on what speed/gear you started they swapped places. After about 140 the GT would walk the Z and keep pulling away everytime. But, some times the GT was playing catch up to do it. The C6 has long tubes, air box, tune. With a pulley tune it would not be a contest IMO. Gearing or not.
I really think the chassis is hard to beat in the GT. Turn in, feel and braking are all way better. The downside is visibility with the big pilars. The car also feels smoother on acceleration, while both are strong. Two different weapons for two different purposes IMO. A true GT class car vs. a no worries track day hero at 1/3 the price. The C6 also makes a far better daily driver, but is not as fun to drive IMO. It's more comfortable to drive with all the creature comforts. If my wife would still drive a stick we would have already added one to the stable.
Handling, C5 vs. the C6 with stability control either is super easy to drive fast on a road course, not as much talent required in comp mode. I did think the C5 was better in transition and easier to toss. I also think the C5 comp mode calibration was better. Through the tighter parts of the track the C5 I thought was better overall. But where I would get up some good speed, the C6 shines and the brakes are way better. It's pretty easy to carry more momentum with the C5 out of sweeping turns, but the C6 had the extra power to eventually overtake on any decent length straight section.
