Now, you could underdrive the MC-E, wiring it in 4P (turning it into a pseudo P7). I don't think we explored that. I like underdriving the P7 more and more since you can still get a lot of lumens out of the emitter with a low forward current (say 250mA or 350mA) and low associated forward voltage.
I don't like building AW towers using MC-Es though. The fit is very tight and I sweat it out every time I grind the MC-E's case to fit the emitter through the SureFire TH reflector opening. Maybe I'll give it a shot (I have an extra K-bin MC-E) and run it in the FM 3xC body with a GD1000. The negative is that you aren't going to get the throw that you'd get with a single die emitter. The benefit, at least for a K-bin MC-E, is somewhat more lumens out (maybe 20%) with greater LED efficiency (lower Vf). If I had an M-bin, then maybe I could get 30%-40% more lumens.