The real problem is you never know what you're up against.
It's like any modded car, really. When you have exhaust on the car it's going to SOUND fast, regardless of whether it actually is or not.
Some GT's will sound really mean but end up only having mufflers. Others might have a **** ton of other stuff to back up the sound, so you never know.
My Mustang... you'd never guess that it pulled 1.9 second 60's all day long on stock tires and could rip just about anything out of the hole. It looked stock and my Magnaflows with o/r X-pipe had a very tame idle.
You'll know when you run 'em if they are stout or not. Usually when you see the front wheels lift off the ground on the launch you kind of get the idea that you're f***ed.
This one is a classic: