I actually just bought one!
As John said they were not to be sold until after the KR conversion was done at Shelby Auto. I also have a twin to the KR I just bought a Red/Silver combo.
Ford builds the car and then its shipped to Shelby Auto to have the KR conversion done. So what that says is its not to be sold or driven until the conversion is completed.
Because the conversion will have its own stripes they are sent stripe delete, floor mat delete etc.
They are rated at 540hp but we all know they make nearly that at the wheels!
Muscle Mustangs & Fast fords tested one to the tune of 11.92 @ 120mph bone stock.
see this article
http://www.musclemustangfastfords.com/features/mmfp_0809_2008_shelby_mustang_gt500kr/quarter_mile_results.html
11.50's on a stickier tire.
They come stock with a 3:73 vs the 3:31 in my other Shelby
They come with different tires and wheels, brakes, suspension, different engine calibration, Ford Racing Air intake, different shocks, a 7000.00 Carbon Fiber hood, bit lower, carbon fiber front air dam, mirror covers etc. They are approx 200lbs lighter than the stock gt500 as the shipping weight on my KR is 3785 vs 3970 on my gt500. And the EXHAUST..... WOW does it sound awesome. Maybe some sound video too.
Will post a few pics and more info in a day or so. r