My engine is climbing in mileage and although she performs the same as new I'd like to have a plan for when she decides to go. So far I've got 246,000 on the clock. The car still drives like it did new but I'd like ore power in the future thus came the idea to build a high performance engine and drop it in. My questions are.
1. What engines are capable of fitting. I have a m54b30.
I know you're probably going to say well any six cylinder engine. Sure, size wise it may fit but sensor compatablility and mounting and transmission. All that has to fit the same.
2. Can I take a s54 motor and drop it in? What kind of wiring nightmare would that cause me.
3.how much power can the stock transmission handle in the x3. It's a five speed auto.
4.how will I retain all the normal functionality of my car whilst having a higher performance engine. I.e., cruise control, etc. I imagine there's a way to use the stock computer from an s54 and the stock unit that came with the car to somehow make that happen. Either that or a re programming of the s54 computer to work with the x3s cruise and such.
I really just want a little more power, the stock 3.0 moves this thing quite well, but a little more would be great.

Someone here knows someone or knows how to do this. I may be an idiot and BMW may be like Honda where you can swap from car to car and it's not so hard. But with all the computers and electronics I just want to have a better understanding before I dive in. It would be really great to put a twin turbo 6 cylinder from the 335i or a s54 turbo. Something similar. Turbos always great, if the tranny can handle it that's what I'll go for. If not, I want to be around 4-450 crank. With the driveability of a stock car.