i would go with a saito .82..... i have one on a .46 UCD which is a little heavier than the twist and it does whatever i want it to do but a little more power to pull out of hovers would be nice and i think the .82 would be a perfect fit for the twist.....you just have to keep in mind not to fly full throttle in normal flight, going vertical at full throttle shouldn't be a problem.

I'm sure the .72 will do a good job but for a little more money you can get the .82 and it will also be a good engine if you wanna move it into another .40 size plane like the Harrier 3D 40, Funtana 40 or similiar planes. The .82 will give you more power for basically the same weight as the .72, the .82 gives you a little more versitility than the .72.