If I were to do that I would have looked for an 11 335is (kinda pricey though), as you get some M stuff with that. You get that dual clutch tranny, better suspension, more power and the 6 or 7 sec extra power boost unique to the is that takes torque up to 370 lb-ft is amazing.

have fun with the n55 engine! My friend has a n54 and he says the n55 are much more reliable and therefore still used in current models.

Darn hate to see you go brother, but like many of us said stay with us an check up on the community. I swear this is the most helpful bunch of people that I have met online. Were can you PM a total stranger, get sound good advice, and throught it all actually have people care about you and your ride with the great feedback. It's pretty special man and hope to see you post soon.

I dunno- the N54 is a pretty stout engine. Forged internals- problems are very rare with the engine itself even with high (15+) psi of boost.

The platform does have other issues though.

-High pressure fuel pump failures (recalled)
-water pump replacements (electrical unit that stays on to cool the turbos after the engine is turned off, wear and tear item, 60k miles est)
-carbon build-up (estimate a walnut shell blasting every 50k miles)
- turbo wastegate rattle (bmw warranty covered to 120k miles)

In my opinion, it's an excellent engine, but be prepared to pay for the maintenance. I'd personally take the n54 over the n55 any day.