I'm not sure how trucks entered into this, but...
With a 100 hp advantage, more torque, less weight, and almost certainly better
suspension/related components, from the standpoint of pure performance? It will whomp a 2005 Mustang GT rather handily (so says anyone who has a body temperature above, oh, say, eighty). That's what one can get if they are willing to spend $50,000 on a vehicle. "You get what you pay for".
With market adjustments the cobra will probably be close to but not quite as much as a 'Vette... we'll see. It will have 450 hp so the performance should be neck-in-neck at worst.
Getting back to $27,000- land, bear in mind the Mustang GT offers more horsepower per dollar than the Corvette, in fact, with the LS1's no longer around, maybe more than any other production car right now.
If GM does bring back the F-Body it will be interesting. That's a big if, too - especially in light of GM's current $$$ woes, though I've seen concepts of a 2007 Camaro. If it happens, they'll be playing some catch up to the Mustang. The 2005 a hard act to follow... but GM managed to follow in the 1960s so nothing is imposible. I would expect that GM would stick to the formula of trying to make a faster yet similar car. How well that might work for them is the question.
When the LT1 was introduced in 1993, it was a big chnage in performance. Up to that point, even though Ford's 302 was making 10 poines less (225) than GM's competing 306 (235), the Mustang was still the faster car. Enter the 350. It pushed 275 horsepower and without question put the performance crown in GM's court. They had it as long as they had the F-Body...
Which brings the point. Yes, after 1993 the F-Bodies were always faster than the Mustang (in 1998, a painful 80 hp faster). And by and large, this market was about performance. But there wwere other factors besides that. The general feeling I get was that the F-Bodies stressed performance at the expense of everything else. A lot of auto reviewers indicated the same thing. Huge hump in the passenger floorwell for the cat converter. Tiny cabin, huge outside. Lots of blind spots. Spoty reliability compared to the 'Stang. On and on.
When I was buying a V6 back in 1997, I myself evaluated and test-drove all three. All had 3.8L motors; The Mustang had 150 hp compared the the F-Bodies' 200. The drive in the F-Bodies was far more satisfying to me; no question they were quicker. But I far preferred the Mustang in every other regard - looks, interior, overall "driver friendliness" if you will. And I think that was a huge selling point to others as well.
So your question: why cant Ford make something to compete with GM and same cost? I'll answer that by asking it rather: why can't GM make something to compete with Ford and same cost?
The Mustang has run unopposed for three years now.