I had a Saito .72 on my US .40. It flew quite well with it, but it had a weird problem which would cause it to go horribly rich and shut off abruptly after running for extended periods at half stick. I had a couple of crashes because of that.

I am now running a YS .63 on the plane with a 13x6 prop. So far this is my favorite airframe/engine combo... it can do every stunt I know (and some I don't ) and runs perfectly.