"Why not try it?"

Why risk the airplane? As for second guessing the designers, some need to be second guessed, as you know if you've been in R/C for very long. A designer's or factory's recommendation is NOT written in stone. How many times have I seen a wrong Center of Gravity recommended? A lot.

A 20 oz. loading on a draggy plane isn't "tame" in my book. Coupled with the high inherant drag of bipes, and the small engine recommended, it's a formula for disaster, in my book. An 8# stunt biplane like the Ultimate, with a .60, is probably underpowered. People are putting 1.20s in this plane, does that tell you something? A 1.20 may certainly be overpowering it, but if it flys without pulling the wings off, that might indicate the "designer's" recommended engine range may be wrong. Is the plane you mention in your post a biplane with a thin airfoil and large control surfaces?

I repeat: an 8# biplane with thin airfoil, high wing loading, and typical biplane drag needs more than a .60 for confident flying.

'nuff said...

Dr.1