Firstly, I believe that there is a message board on this site for discussion of cars similar to the M5. Apparently, more than a few have failed to notice that there is a better place for discussion of other cars.
More than a few have also been dissappointed with the "relative" value of their M5 compared to an Audi S4, or other cars. I have a 2000 M5, after selling a 97 Viper GTS. Now, when I had the Viper which costs $70k, did a Porsche 993 TT owner think that he overpaid at $120k, as we had similar performance? No, I don't think so. Before the Viper, I had a 96 993 (no TT) which costs $70k, did I think I overpaid because an M3 or a Corvette had similar performance for $30k less? No, I did not. No argument that for those wishing to upgrade, bang-for-the-buck always goes to Turbo cars (although reliability and warranty may be a problem for you, as I personally know). Hey, if bang-for-buck is your thing, throw nitrous on you car, and go bragging.
Yes, I too wish that the M5 didn't provide such smooth and consistent power from idle to red-line... but that doesn't mean that it isn't fast... just refined. The Porsche 993 I had wasn't any faster, but sure sounded that way. And those 4.5 second runs to 60 in a chipped 4WD turbo car... only possible side-stepping the clutch at close to redline (your car will be in the shop more often than not). Try a normal launch, and the chipped 4WD cars aren't so special.
Just my opinion, and I will be happy to discuss further on the similar cars forum.