I should have stated that while the plane flew "well" on an OS 1.60, it didnt' have much excess thrust and had a hard getting out of a hover. From a cruising speed straight and level it would climb vertically maybe 300' or so before running out of steam.

My OS 1.60 swing an APC 18x6w (about the same load as a Xoar 20x8) at right around 8600 rpm tuned down from the ~9000 rpm peak. No 30cc gas engine on the planet can touch an OS 1.60 in terms of power. More CC's are definitely required because as they say, there is no substitute for cubic inches (you can always throttle back).