I would second jhurless above. I was going to recommend a 2001-2003 530i with the sport package. It will be fast enough, but not as fast as the 540i. But also won't have the terminal timing chain issues that a 540i (or 740i) with the V8 will have.
Go drive one. When you're serious come visit us, and we'll help you find someone to check it out for you.