My guess is emissions is a big one. I'm not saying you're wrong, merely offering my observations. It's not night and day going from 195 to 180, but before with stock fan settings on the Z06 it was an absolute turd at 220 when autocrossing even though ambient was in the 30s. You have to consider the factory's objectives vs your own when choosing an operating temperature.
if your Z06 was a dog at 220° it wasn't due to the engines temperature. That isn't even that hot