3D2000,

I have been flying my knife with a TT Pro .46 and APC 12 1/4 x 3 3/4 prop. Plenty of power, hovers at less than 1/2 throttle and climbs out of hover like it was shot from a cannon. My friend with the Su-du-koi ARF flew his with an os .46 fx with the APC 12 1/4 x 3 3/4 prop, same results. Plenty of oomph for this plane. The Top Cap at my field flies with a Rossi .45 and tuned pipe,not sure of the prop but somewhere in the APC 11 or 12 inch range, also a good combo. For my Top Cap ARF I plan on using my MVVS .49 with mini tuned pipe or my TSI .46 not sure yet which one.
I don't really have any experiance with the Magnum engines, but any good .46 should be plenty for these profiles. Definately go with the APC prop either 12 1/4 x 3 3/4 or 11 x 4, whichever your Magnum can spin up faster. Buy one of each and see which one your engine likes better.
As far as the four strokes go, I can't be too much help. I've never flown any of the "smaller" four strokes. My friend with the Su-do-koi had the Saito .72 in a hanger 9 pizzaz, he wasn't all that impressed with the plane or the engine, he sold both after about a week or so. I know alot of people are raving about the Saito .72 but i've never really played with one enough to give you an informed opinion.