ORIGINAL: aspeed
It is about the same price as an OS .55 or Saito around here. I think the profi would be better to get the adrenaline going. The only thing stopping me besides the price and wife, is our club rules require a muffler (piped?) and a means to cut off the motor. I think that may be good for me anyway in case it gets ahead of me.
Then you need the piped version when it comes out in January!
It should be easy to rig inflight cutoff, you'd need an additional micro servo and some trickery with a tee fitting in the fuel line and a dump port with releasable tubing pinch wire. The FF guys do this with flood offs and timers.
I've never heard an IC engine run at 45k except F2A videos on Youtube.. I feel the need to experience it live.