I'm not a fan of the back of the S550 chassis, but congrats on the new ride!!
I had a 2012 GT before I got the SHO. The SHO beats the GT as far as creature comforts go, but the GT was faster, both stock and tuned, than my SHO is.
2012 Mustang GT Premium, factory 3.73 gears, Brembo brakes, comfort package, HID package, Boss 302 Laguna Seca 19x9/10 wheels with Pirelli P-Zero rubber 265/35ZR19 & 285/35ZR19. The only mods I did were a Roush Axle-back and MGW shifter.
Stock 13.05 @ 108 mph (MoKan dragway)
Tuned 12.59 @ 113 mph (MoKan dragway)
2014 Taurus SHO, all options except performance package, only mods were to swap the stock wheels for a set of 2010-2012 20" wheels.
Stock 13.79 @ 101 mph (MoKan Dragway)
Tuned 13.04 @ 106 mph (Hartland Park, Topeka)(I had some driver errors all day, and at least an hour wait between each run, so there's room for improvement here)
My 60's were about the same in each vehicle, but the SHO weighing a good 1000lbs more than the GT really tells the tale here.