On my UCD 60 I had a saito 100 and it had good power for 3d it would hover around 1/2 throttle but I am NOT at a high altitude like you also once I had it broken in and set-up right i never had problems with it inverted. And yes I would always go four stroke glow for that size plane. at your altitude I might go with a saito 150 for the UCD or a 180 for the funtana (I belive the funtana is about a pound heavier)