This will be a rather unique comparison. I can't ever remember two cars that were so mechanically similar from two different manufacturers.
There horsepower and torque are essentially equal, same basic curb weight, very similar tire footprints, nearly identical gearing (the spacing is the same and each ratio is within about 0.03 or less), nearly the same rear end gear (3.42 vs 3.55), both front-engine / rear drive, manual transmissions, length and width of the bodies are within an inch...pretty remarkable.
With two fraternal twins (or brother from a different mother??) competing like this, I can't see any real way to figure the winner based on numbers. These cars are just too similar. It's going to come down to integration and finesse, which ever car is best balanced and able to put it's power to the ground.
The ZR1 has been in a few recent comparison tests, both against other cars and other Corvettes. In a recent comparison between the ZR1, McLaren MP4-12C, and 458 italia at Spring Mountain (Road & Track: Oct 2012, Steve Millen driving); the ZR1 was quicker than the 12C, but slower than the 458.
Against other Corvettes at Spring Mountain (April 2012, Tommy Milner driving), the ZR1 was about 0.85 sec slower than the Z06 (and the ZR1s lap time was 2 seconds better than during the October test).
Spring Mountain is a tighter course than Laguna Seca (I think), but it's clear that there is plenty of variability session to session.
In any case, we'll find out soon and who knows what kind of times these cars will put down on the actual day.
I'm guessing that these two will be within a few tenths of each other and I'm still thinking the Viper could win.
I can't stop thinking about it this weekend, but it will be exciting to finally know and see some real numbers.
-Nick