Got an '06 M7 I'm working on right now that's heavily modded, same issue. It's a LOT more complicated than cans, clutching or intake. '06 model was notorious for bog at about 7000 rpm. Power valves aren't opening, could be cable adjustment, servo motor, ECU, stator, voltage regulator or wiring harness issue. Could also be ignition coil as I've heard of it causing the problem as well. Good luck finding the gremlin! Will update with what I find as I work through.