Eh, the 2011s were around that zone at the wheels add a few more pounds and IRS? Not a surprise.
Honestly, I wouldn't be surprised if stock for stock a 2011 would beat a 2015 if only by a slight margin. (Assuming no one uses launch control or whatever, so apples to apples!)
Yeah you might be right. The extra weight could potentially offset the 15 hp. The gt still has plenty of hp per dollar. Worth it even if its not any faster.