A Brison 2.4 (40cc) is absolutely the top end power-wise on this airframe.
I have had all sorts of wood & metal parts break on me because of excessive power on mine.
(And I know how to use the throttle, BTW) These were not crash related failures.

Going to this much power results in a high maintenance aircraft.
I've parked it for now - Tired of messing with it. (Not a sucessful project because of this)

I was turning a 20x8 at the low 7000's. (600ft MSL)
Out-of-sight verticals with this setup.

In hindsight, a lightweight 25 would have been a better choice.
Keep the weight below 12lb, whatever you do.

A 50cc at any altitude would be insane IMO.
If you really want a biplane for this size motor, I would suggest another airframe.
Have a look at the Procraft Ultimate or the Miles Reed Weeks Solution.

Good luck, whatever direction you choose. Post some pics!