Let me just say that the Northstar V8 STS's are an absolute BLAST to drive. They are plenty fast, and yes they do surprise a LOT of people when they hear than engine roar to life and your car suddenly flies by them lol
As others have said, be safe/smart, keep your car in Ds, and shut the stability/traction control OFF (press, and hold the t/c button), and HOLD ON !! As for the comment about the Mustangs, in my experiences, these cars are just as fast as your common V8 Mustang (NOT the Cobras, GT500's etc. though obviously).
JUST my thoughts on the matter
Now, if your REALLY want to go fast, then I suggest you test drive a CTS-V. . . . . .WOW, now THATS fast lol