I second what NAS19320 said (I have that same combination) and agree with Ed Moorman's comments as well. If you stick a larger engine in it, you'll have to add lead to the tail. The added weight will take away from the flying qualities.

Mine flies like a raped ape with the TT.46 and I have a ball with it. Great combination.

I have Saito .82 in a Funtana 40, so I have a feel for the power of the Saito... too much power for the 4*

Bob