So you're not looking to get a 370z at all? In all seriousness, I'm curious why you're on here? I mean it's fine and nice to have more knowledgeable people on the forum (based on your pasts posts) but what brings ya here?
I was strongly considering a 370Z a while back, but decided against it. I stayed because the forums are lively and in general populated by agreeable people. Lots of "car" enthusiasts here.
I am going to contest your claim that the '11 GT is a direct competitor. First, of all the '11 Mustang GT is NOT a sports car, the 370z is. In fact, there is no reason why these two cars would even be cross-shopped unless you're looking at a particular price range for cars that boast
performance. If you're looking for a sports car you're not looking at a Mustang. If you're looking at a muscle car you're not looking at a 370z. Just saying.
Why isn't it? Because it has 4-seats? So does the GTR. Also, the BOSS has a rear-seat delete option from the factory, making it a 2-seater if you still want to contest the point. Also, it will pull 1+G on the skidpad, and has 47/53 weight distribution, or near, from what I remember. The only reason anyone would say it is not a sports car is because TRADITIONALLY, it was a pony car. However, in BOSS form, I think it every bit a sports car, and if you want to stretch the definition a bit, in GT form as well. It will do anything the 370Z will do.
However, you're correct. If you're looking for a pure performance vehicle the Mustang GT is significantly faster in just about everything, even for a *gasp* muscle car is still edges the 370z on a track (on a tighter, more technical course the gap is significantly shorter) due to it's power advantage. Also, despite it being a SRA setup, the Mustang GT actually handles impeccably well and it's a pretty good driver car.
Now, looks wise, you cannot really compare although I will say I've gotten quite a few stares and compliments on how it looks. The problem that you'll find with the Mustang is, unless you've got an exhaust that deafens everyone in a three or four block radius, the car doesn't stand out like the 370z does.
All in all though, performance stats aside, the Mustang GT and 370z, when looked at rationally, a logical deduction concludes that cross-shopping them makes little sense unless you're simply looking for the fastest car under $40k.
Which again, makes me believe, that Nissan won't do anything performance changing for quite a few years to come.