Having had both the Easy Sport and a 4*.40, I say go with the 4*.

The Easy Sport is a great plane and I enjoy flying mine (ARF version). It's easier to fly then the 4*, but I don't think it's much different in performance than the Avistar. Might not be enough of a new challenge for you.

The 4* though would be a great next step. Low wing, tail dragger and a good step up in performance. This is my favorite plane. If I were to do it over I'd also go with the .60 size. Laser cut wood and only about $50 more than the .40 size if you go with a .75 2 stroke engine. Much more bang for the buck!