I fly my 12S E5 with 556 at 2450 rpm. I've used anywhere from 2200 12S up to 4400 12S. The sweet spot is around 3000-3200. With a little more weight it performs really well and still retains a ton of pop. Even with the 700-sized 4400s it flew amazingly well, just a little mushy on quick collective inputs. Recently, I prefer the 3200's as they give the best performance overall and can fly for about 4:00 on the timer.