I'm curious how much faster the Corvettes (or other cars) would be with R-compound tires. I could see a standard Corvette Z51 with R-compound tires pulling similar lap times around a track as a factory floor Z06. Of course that's a bit of a problem when comparing ring times. I might consider say a Miata stock even if you put new tires on it. However, when we start playing the ring time game are we really talking "factory floor"? How much of the various lap time differences are due to tires vs other factors? This is why I have heard people say the car magazines should compare cars with the same tires. I also suspect really grippy near R-compound tires is PART of how the 911-GTx's have turned such fast lap times. I suspect if the previous Z06 times was on run flats the car probably left some speed on the table.
Lots and lots of variables. Either way, I guarantee my magazine is faster than yours!