Another soul living with a pretty high field elevation...

We're at 4500' ASL here too and you'll find there is a definite "hit" on the performance especially in the Summer when the density altitude goes way up due to the higher ambient temps.

I'd forget the three blade prop as they are less efficient than the two blades as you seem to realize already, but the difference is more noticeable with your altitude. Also, while I'm not familiar with those engines the guys around here who have or do run them say they really like the higher nitro content fuels. The one I saw a LHS guy fly (it was one of the older original ones) said that they tried several different fuels and the engine really woke up with 30% heli fuel. This guy is a really good pilot with Giant Scale as well as doing much better than average with heli flying, and has lots of experience with all sorts of equipment so I tend to put a lot of faith in his opinions.

I do know that the two YS-110's I still have around, run substantially better on 30% nitro than they do with even the 20% fuel. If you do experiment with the different nitro content fuels, you'll need to reset the needles when you change from one concentration to another... [8D]