My favorite feature is the 600 lb/ft of torque the highest of any Naturally aspirated production engine. Oh yeah, and the 4.9 lbs per HP!! I also like that they made the traction control and launch control selectable so when I dream about driving one I can turn it off.
http://www.autoblog.com/2012/04/04/2013-srt-viper-bites-back-with-640-hp-returns-to-racing-w-vide/
http://www.autoblog.com/2012/04/04/2013-srt-viper-bites-back-with-640-hp-returns-to-racing-w-vide/