If you want to switch stations, toggle the rear demister etc etc, isn't it better to have one specific button where you hit in a split second rather then have to 'idrive' thru the menus? (ok I only tried the first version idrive on the 7 series, not sure if they changed it. Can't see how though).
Its like the old PCs where you just hit the power off button and it goes off compared to the new PCs where you hit 'start', then hit 'shut down', then hit 'confirm shut down'. Which is faster?
As for M3 vs 335i, I'd rather take the E92 335D. Bags of torque.