Screaming engines are OK for Pylon racing but usually much less efficient for pattern. Horsepower generated at 18,000 rpm is pretty useless. The EU1-A needs a lot of thrust, the screaming only happens after the crash . The YS FR was significantly more powerful than the OS 61VF - I ran both until the OS 61RF-ABC-P was released. The YS was still very powerful even with a 12x9 prop!
Try all the engines and various props (I know, easy for me to say...): 11x7 to 13x9.
Post some photos of construction and the finished airplane; we'd all love to see!
-Will