Avistar is a top wing trainer. Assuming you are very comfortable with the Avistar then you could try the Caos but maybe with a 40 sized motor (.46) or Super Tigre .51. The caos was a design of Joe Bridy who long since sold rights to his designs. I am pretty sure this is 90% the same plane that it was. I have a 60 sized version and it tweighs all of 5 pounds. I put a ST90 on this and it basically drills holes in the sky. It is a comfortable flier that flies like it on rails and will take on as much power as you throw at it.Assuming you do not demolish it, you will probably wind up keeping this plane around for a long time. The .51 Super Tigre or even the OS .60 would be plenty powerful but again you might want to start with the smaller motor first.
I think i've pretty much made up my mind on upgrading from my Avistar 40 to a Tower Kaos ARF. The dillema I am having is figuring out what a good engine for it would be. I was thinking an OS 55 however I was unsure if it was going to be too much power for that plane and also for my skill level?