Originally Posted by Fabrik8

Yes... You'll make the same power with either one (turbo, super, etc) at the same boost. You're forcing more air in under a certain pressure, and it doesn't matter how you do it. However, the power bands are different for the two. A s a generalization, superchargers tend to have more low end power, and turbos generally take a little time to spool up. There are a lot of turbo options though, and not very many superchanger units to choose from.
As far as your M3, if it's tuned for 6 PSI without danger then you're fine.
I'd talk to some M3 owners and find out what's out there for your car and what the safe operating area is for a stock engine. The best source of info to start with is people who've been through it already with the same car.