Well, here's a video that I found archived, i've had it a while, and I dont remember the description very well, but, basically, they start around 100mph, the cobra pulls pretty good, then the z06 pulls almost even, then when shifting to 5th the cobra pulls away. So, yes, a 4.6 stang 'can' beat a z06, they're not unbeatalbe, but they are very damn fast, and a 2V GT would have to be greatly modded to be able to run with a z, however, I would'nt say it cant be done, anything can be done.
Anyways here's the video:
http://media.putfile.com/03-Cobra-Z06-Race-Very-High-Speed
Also, here's a pic of me with my friends 04 Cobra, 607rwhp, I dont beleive he's raced any Z06's, but, another of our friends has a very sick ram air firebird, and, well my friend, the one with the cobra, well, alot of his motivation to get his car fast is because of the firebird, it's very fast, lotta money invested. This car i'm sure will eat a Z06. He's not even a very good driver, and he was running high 11's with the car, all day long, actually kind of ridiculous, he made like 15 passes the one day heh, no doubt freakin' quick, would easily take out the vette, however, considering what he's invested, he's probably paid near what a Z06 owner would. He didnt just work the motor, he did his homework.
Sry for long post, here's a pic of the car, bad view but, man sick car, my car feels so slow compared to it.