A few minutes of an interesting read..... GN's much faster with a lot less money, but couldn't compare on a road course. Seems the 2013 Shelby would give these 2 a run for their money with a few thousand $ in bolt ons and suspension work, for about $40-60K less
http://www.motortrend.com/roadtests/coupes/1212_2013_chevrolet_corvette_zr1_srt_viper_gts/
http://www.motortrend.com/roadtests/coupes/1212_2013_chevrolet_corvette_zr1_srt_viper_gts/