The .56 will NOT be overkill for this plane. I'd dare say that the .56 is not overkill for anything larger than 1/2 A (Tongue in cheek). But, for real, anything in the 5 lb class will be suited nicely for the saito .56. Anything over 6 lbs is almost too heavy for this engine. It's a very capable little engine, if fitted on the right airframe. I originally had mine installed on a contender kit built that weighed in at around 6.5 lbs. Although the engine would fly it, it wouldn't do so to my liking. It took quite a take off roll to get it going, and wouldn't pull it very fast at all. Vertical performance was non existent. I finally put a .72 on the contender and really love the airplane now. I put the .56 on a little .40 sized low wing stick that weighs about 5.5 lbs or so (maybe a little less), and it's a perfect match for the engine. Still not unlimited vertical, but much better than before. Plenty of authority for the lighter airframe! Go with the .56, and you'll be excited!