I could be wrong but I think the RS is the 6 cyl. = dog. GT's are alright 0-60 about 5.5-5.8 depends on who's driving. The new cobra's are pretty fast 0-60 around 5.1-5.3 and with independant rear suspension now. They actually handle pretty good. I hate magazine's they are very biased so I never go by those times. These times are from the strip and multiple cars and drivers, I don't remeber 1/4 times off the top of my head. Z's can give them quite a run if not beat them when they are stock, but after a few mods watch out. Remeber just because they are loud doesn't mean they are fast. Lots of kids throw flowmasters on them and consider them modded, in reality maybe +5rwhp difference.
Sure, if you spend enough on your Z, you could give a stock, unmodified 'Stang a good run. But you can't fight basic physics -- the Z's motor gives up alot of displacement to the 'Stang's, so challenging them probably isn't a very good bet. Enjoy your Z, and don't put yourself in a situation that you can't win!!!!
Chuck have you ever heard of power to weight ratio
This is what enables Z's with less cubes to beat mustangs and camaro's. I totally agree stock to stock the muscle cars will win a drag. How many stock Z's do you see driving around that actually want to race, and how many stock Mustangs and Camero's. I run into very few, most of the stock ones do not try and race, they are people who just like having a little more torque than most street cars. I own a highly modded yet street legal (I guess) Z and a mildly modded Mustang with the 5.0. To keep it short my Z eats the mustang and craps it out the exhaust.