We couldn't believe the amount of cars last night we ran across that were willing to run on 95 near Miami. I was in my friend's E46 M3 and we came across a Porsche 944 that was nicely modded that walked us decently hard...too bad I didn't have my car. Destroyed an A6, Magnum, Chrysler 300C, 350Z, other various fart-can ricers, G35's....etc. Unbelieveable.
As far as the M5 is concerned, you'll need to be putting down 380+ whp to run with a stock one. They are no joke.