i just use german castrol 0w30 and couldn't be happier. I would try the 5w40 next time though if it's better for our warmer temps in FL
It's usually on sale at autozone or advanced autoparts for $32.99 5/qts w/ an oil filter.
E90 LCI M3 7-DCT Interlagos Blue/Novillo Silver
[MS Pullies|K&N drop-in|Test Pipes |Evolve Stage II tune|Evolve Servotronic Map|Evolve M3 GTS-DCT file]