I am running an OS FX46 with an APC 11-5 prop on the WM SS. Awesome speed and performance with this prop. I Personally I would avoid the Magnum engine. The TT is a far better value even if it is more pricy. I have run into quite a few of them as an Instructor and they are easy to adjust and produce good power. Saitos are a fine engine but I can have two 2 strokes for the price of 1 Saito! As Piper mentioned, a tach is "very useful!" You can see exactly what is happening with a 2 stroke which makes it easy to adjust. With 4 strokes the sound doesn't give much of a clue as to how fast the prop is turning. A tach is the only way to really tell.