Not sure what year 540 you are looking at but you can see what HP potential you can get by visiting this website http://www.jimmy540i.com/
He has a Dinan modified 540i that includes a Dinan supercharger, chip, intake, high flow intake, blow off valve, throttle body and so on and so on. He claims to have 454 hP and 406 ft lb torque. No doubt he spent a small fortune. I must say that, in my opinion, BMWs are one of the best cars on the road. I will never, ever, ever own anything but a BMW. Next stop, M540. Yeeehaw!

Good luck with your quest for the ulitmate driving machine.

Michael