That’s not true. There is a whole story on why the numbers for the ring were never published and it involves a lot of bad luck. Look up Jim Mero who was a test driver for GM. They actually ran a Z06 at the ring in 7:10. It is an interesting read. 

I would be shocked if it is $5k over what the C7 is. I could understand a special edition Z06 or ZR1 being over $100k but the base will be around $66k give or take. GM is not stupid enough to price out their buyers.

The overheating issue for the Z06 was fixed in the 2017 model year for cars with the manual transmission. If you are buying a Z06 for the track it should be manual anyways.