Yeh well I BROUGHT my GT back in 01 and I think it can kick your Mach's @$$. Dude, calm down...don't take things so personal. Just because someone likes the Cobra better doesn't mean you can't have your opinion.
Simple fact is for modding potential the Cobra is going to win out...period. You already have a forged engine with a S/C, and a stout transmission. Slap a Kenne Bell on there and you are knocking on the 700rwhp door. You simply cannot get that with a Mach with stock internals. The only weak link I see for the Cobra is the retrofit IRS.
The Mach is without a doubt a killer car, and if it would've been out when I was in the market, that's the car I would've bought. It runs in the low 13's in stock form, has nice seats, solid rear axle with 3:55's, and killer looks. The modding potential for the Mach is good, but not as good as the Cobra due to the 3650 tranny, and relatively weak internals.
So basically it all depends on what your budget allows for and what you are looking for in a car. Go test drive them, and decide for yourself which one fits you better.
P.S. On the money thing....I know for a fact that I could walk into my local dealer this afternoon and drive home in an 04 Cobra for $28,000 and they are the only SVT dealer in this state.