RE: what engine ?
Use the Magnum 46
Prop with a 9x7 or a regular 10x6 prop to start with.
If you enjoy the combination and want a bit more speed, buy a jett-stream or ultra-thrust muffler and bolt it to the engine - instant 1000 rpm boost (+) - no hassles, just bolt it on and go. Keep the same prop sizes.
The SK engines i am aware of have shown a tendency not to run well at higher rpms (which is why they suggest the bigger prop)