Any BM swap that doesn't involve an S85 is a waste of time
I kid, kind of.
Though if you are actually serious about it - it really depends on what type of power you are going for. And if you are willing to live with a Motec or PROefi.
If your goal is HUGE (four digit) power, the 54 is without question the motor of choice right now. Outrageously overbuilt from the factory, and takes very well to boost for such a high-revving NA platform.
Edit: just realized I bumped a week old thread. Sowwy.