If you want the Ultra Stick to perform well and be able to hover and to all the aerobatics its capable of, then you'll probably want to go with a Saito .72 or YS .63. I have flown the US 40 with a Saito .72 and it gives great performance. I have also seen many fly with .46 or .50 2-strokes and they don't have enough power for things like hovering. The only 2-stroke that i see hovering the plane is a Jett .60 and its more money than a 4-stroke. Plus the 4-stroke is quiet and won't cause any noise problems at your field.