You can make any car fast if you throw enough money at it....
The base price of both is within $500 of each other, but when you option them up, the GT500 is way more. Plus, the Ford dealers won't budge on price. I test drove the Shelby with all the options I wanted and it was $67,090. My ZL1 stickered at $58,444. I paid $56,000 and had $1500 on my GM card, so $54,500.
I think they are both awesome cars, but I don't think the GT500 is $67090 awesome. It should cost 60 even, with all the options.