I'm particularly curious about traction and handling between the two on stock wheels and tires. I've owned a 1999 Cobra, but I've never been in a newer Mustang. I'm wondering if the stock GT needs upgrades to grip and handle as well as a 99 Cobra, or if it's been improved over the years to the point where it's already as good or better.

 

Depends, the chassis in the S-197 is way ahead of the SN95/New Edge cars (even with the IRS, but that has more to do with trying to fit a square peg in a round hole). That said, the 05-09 cars were dampened/sprung to softly and hobbled with all-season tires. The base '10 cars featured some improvement in suspension tuning (confined to the rear mostly IIRC, when Groot posted here he made mention of it). However, if you can get a track pack car then the issue is moot.

 

how about 99 cobra vs. 11 V6?