Of course this is all personal preference, but I would have to say that a .90 size 4 stroke is a very versatile engine. There are a ton of airframes for it so you can be flying something new all the time! Also that size engine gets you into a larger sized plane and as you know, bigger planes fly better than small planes. If I was told that I could only buy 1 engine for the next 5 years of flying excluding gassers, it would be a 90 sized 4 stroke. BTW, I have an Enya .90 on my Sig Astro Hog and it flys it great. It should do a fine job on a Hog bipe.