This is not my bias because I was hanging out with the Viper Racing League last week, but if you guys check out this months issue of Car and Driver magazine, they review the Z06, 911 GT2, GT-R, and Viper ACR. In almost every track/speed/handling category the ACR is faster by 4 seconds if not more. However, the magazine chose to give the first place review to the GT-R. Where the GT-R earned the most points at was not in performance, but in stupid amenities such as comfort, appearance, color, etc. If you want to review a car for its physical appeal and eye candy, say so. Do not blur performance review with style because those two are different things (show mods verses tuning anyone).
Anyway, summary of rant. Viper ACR is faster than GT-R, 911, GT2, and Z06. Read this months Car and Driver. Viper gets shafted.