RE: Ultimate biplane, mid-sized arf.?
I agree with you. I am not recommending the use of a .91 four-stroke.
Mine (kit built) was powered with an Enya 1.20R four-stroke. Mine latest one, an ARF version, will be powered by either an OS FS 1.20 pumped four-stroke, or by a Saito 1.25a. Who knows, my Super Tigre G2300 (1.40) may end up on it if I'm not satisfied with the power output of either four-stroke.
Ed Cregger