I flew my Avistar for 3 years and loved it. Fixed the wing so many times I don't remember how many times. Its final demise was the last crash and I just didn't want fix the wing, it had more glue in it than balsa by that time. I flew it with the Thunder Tiger GP 42, and it flew just fine, even on windy days (20mph+). It wouldn't hop off the ground like other Avistars with 46s in them or fly unlimited verticals. The TT GP42 is very similar to the OS 40 LA, bushed no bearings. I think either is a good choice. They are good little motors that are dependable. A 46 for a few extra bucks will give a real punch to the performance, but will also burn more fuel. You might want to look at the GMS 47. I just bought two and installed one on a Tower Trainer. Plenty of power, starts easy seems dependable and they're a little easier on the wallet. Go with a 46 if you can afford it, it will fly just fine with a bushed 40 like a TT GP42. An additional note---> I learned on a Sig Senior Kadet powered by a TT GP42. Yeah it was slow, but it flies just fine.

Good flights to you,

Tom