08 KR vs 08 vette
 

http://www.youtube.com/watch?v=WIPBP-9TUnQ&feature=fvw
probably a repost but what the heck. How much more tire is on the vette over the KR? I wonder what would happen if both cars ran the same tires?

Not much - wider tires with the same O.D only change the bias of the contact patch (but a taller and wider tire would put more rubber on the ground), the glaring issue with the Mustang rear suspension is probably the RUCA (which isn't helped by the GT500 or KRs heavier front bias), fix that and it might be a different story. All though hacked into oblivion, there is a video of an 3.73 equipped '10 GT with an O/X-pipe and aftermarket RUCA getting right into the 12s