I am not familiar with RMX or SC engines. The engine of choice over here in the 40-46 size is the OS 46AX for both sport and trainer airplanes. We can cheaper engines but the AX engine is very user friendly (easy to adjust and reliable running), is a very strong engine and is used for both sport planes and trainers. The OS LA engines are reliable but very weak running. YOu are looking at least 2000 rpm less with that engine than the AX in the same 46 size. Once you see how easy the AX starts and see how it spins the prop you won't want any thing else.