If you really want to modify the N52, contact RMP. They are racing an e90 with the N52 and making quite good HP. I do not want to quote and figures or modifications as it's been a while since I've spoken to them.
I think I remember cams, headers and piston/con rods as well and reving to 8,000rpms. Don't quote me on that for sure though.
http://www.rmpmotors.com/