A few years late reply, but i found it interesting how PD messed this up.
Irl the Z06 was the GT1 and the ZR1 became the GT2. With the GT2 being the slower one, and less downforce.
The ZO6 RM has a wrong body model. It has the GT2 model instead of the GT1
Both just use the GT2 model, wich btw has the wrong rear difuser. It has the defuser of the GT1.
I really do not understand how PD could mess stuff up this bad. I wouldn't call my self a true fan, but i allways liked the racing Corvettes, so i hope PD will fix this in GT6.