At your elevation a 50cc gasser is going to give you the performance you are looking for. The OS may be a little weak at altitude. With a gasser you can run a smaller fuel tank. I had a DP Extra with a Moki 1.8 and it would just barely pull out of a hover at sea level. I sold it to someone who put in a 50cc gasser and while the plane was a little heavier, it did fly better. The plane snap rolls weird though. I bought my plane used and it had CA hinges. They did fine until one day I did a tumble and all of the rudder hinges snapped. Fortunately I was able to land it.