Heli,

Just my humble opinion, but I have had the OS46FX in a 4Star 40 and it was great. The plane had some mods that added weight and the wingspan was stock, so there was both weight and drag and the 46FX pulled it around with authority.

If you are looking for an engine that is versatile enough to allow you to grow into the popular 3D birds out there I think you will find that the 46FX will do nicely. I took that same engine out of the 4* and put it on a Profile Sledge 540 (that I built like a brick 4.8 lbs.) and it will hover 6" (not by me though[&:]) off the deck with plenty of pull-out. The new AX is getting good reviews from the 3D guys as well. I have one going into a Burrito this week, so I don't have first hand knowledge....yet. There are still plenty of 46FX's out there and the AX is priced nicely at $109 from Tower. I got mine from the LHS for $103, so I guess it is pretty even when you compare shipping costs to our obscene state sales tax.

Do what feels right to you, but just thought I would throw that in for you to consider.

Also, don't forget the thrust and or speed that can be gained from experimenting with props!