I have an e46 330i as well, and my mentality was to stay with an engine who's problems I've worked with before. My 2005 3.0 does not have a problem getting out if its own way by any means. What's interesting to note is that the differential and final drive is higher in the 3.0, meaning higher torque to the wheels. For this reason, the smooth high revving I6 gets to flap it's wings, relying on engine management and a light foot for efficiency. This compared to using gearing against a high torque motor to reduce rpm as seen in the v8.

Finding a well optioned late I6 was a struggle for me (sport, premium, nav, pano, 19s, truffle interior), especially in the sub 100,000 mile range. It's a race to the bottom now as the few lightly driven x5s left will start creeping over.

That is my personal take on the subject, and I'm sure you'll gather that the decision must be made after driving both.

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2006 e53 4.8is Imola / Cremebeige
2005 e53 3.0 Black / Truffle - AT, Sport, Premium, ZCW
2001 e39 M5 Black / Caramel - Extended Leather, Premium Audio