I had an APC 18-6W prop on my Saito 1.80 powered G-202 and the performance was similar to what you described. Using 30% nitro fuel, it would just barely hang on the prop at about 3/4 to 7/8 throttle with little reserve for recovery. I don't think you can get unlimited vertical out of that combination. Good flying airplane until you attempt some of the more power demanding 3D type stuff.