The 4.6 would be a better platform for turbo... there are plenty of turbo M62 motors running big power.

I personally would put the $ into an E36/E46/E90 and boost the shit out of it...

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2002 X5 4.6is - Titanium Silver / Black Alcantara - Dinan Stage 2 - Bilstein/Eibach - Brembo BBK ----SOLD---
1993 318i - Brilliantrot / Tan - bone stock daily driver