I would go with the AA tune. It provides the throttle remap you get from the PBX along with some performance improvements. If you decide to get the 3IM later, you won't have to wry about getting another tune.
Montego Blue Metallic e92 6MT
|| BMW Performance SSK Kit || Charcoal Delete w/ K&N Drop-In || CDV Delete || Custom Clutch Stop || (3) Stage Manifold Swap || Stage 2 Eurocharged Tune (