One of the reasons for high rpm is that all events are timed from take off to touch down. Most events are lost by the time it takes to get to manuever altitude and to return to the ground after the event is concluded. I know Gary Wright has been playing with some very high amp draw systems. I had Model Motors make me a version of their "Extreme" with a 3.84 gb instead of the normally supplied 6:1, but we're still only looking at 13.5K at the prop. You might want to look at the Hacker B40 series.
For Sport Flying a Comp Fun fly plane, I like around 12 cells and the MaxCim "D" system, but the larger prop size affects loop diameter and therefore longer loop times, it wouldn't be competetive.
For competition, I think the ideal combo would be about 100A and 6 - 8 cells. That way you could keep the overall weight down. Run time needs to be around 60 seconds max, with the JLS Combo requiring around 40 sec to complete, you probably get away with 50 seconds.
We're looking for some competitive E powered planes for the E Cubed R/C Challenge. More info at