To me, I see a Roush as a waste of money (at least the Stage 2 offered in California). You pay a premium for the name and really could do a lot better with a off the floor Brembo GT and adding a Griggs SS suspension (or something along them lines).
TRZ06, I totally agree. I would not buy the "Stage 2" Roush. Just pointing out that California drivers don't have the opportunity to buy the 5XR. I'm having a hard time deciding between a GT500 (as a d/d) or a GT of some type (including the BOSS if I can find one in Northern California when they start shipping). Either way, the car won't be a "garage queen" awaiting the day it is worth more than the purchase price. This car will be driven. And enjoyed. It is just such a headache making the choice.
One other poster here (one or two above mine) points out the prices one can have a GT500 for. Yes, they are somewhat less if you buy used. But if you are in the market NOW for a Mustang, the 2011 GT500 is an excellent choice. They are not discounted, but they are markedly improved over the 2009 and 2010 model years (more horsepower, lighter front end, better handling, etc.). They are a more developed car than the previous years. I don't see any reason to refer them as "old technology" when they have aluminum blocks with some very advanced cylinder material (and more horsepower to boot).
But, yes, you do save about 10k - 15k if you get a GT or BOSS.
My point is the 2011 GT500 is in a new class itself, having several engineering changes made to it as well. And the GT / BOSS is a beautiful (both visually and engineering wise) platform for Ford to further in the future.
Just my $0.02 worth, YMMV.