I run RLI Bio-Syn 5w-40:
The UOA results I received back were stellar, making the slightly higher cost of this stuff (~$11.75/quart) much more feasible. Furthermore, the oil runs cooler than most "synthetics" so that should really help you out given that you're running upgraded turbos and higher boost.
'07 E90 335i - Automagic - Non-sport
Cobb AP|Alpina Flash|VRSF 7" FMIC|VRSF CP|TIAL BOV|cp-e DCI|Bilstein B6|E93 M3 FSB|SP Lowering Perches
Summer: Sonic Tuning ST100 - 18x8.5 ET35 - Conti DWS 245/40/18 - 10mm rear spacers
Winter: Style 159 - 17x8 ET34 - Michelin X-Ice Xi2 225/50/17 - 15mm rear spacers