The BME 50 should work fine. The weight of the engine used goes a long way in determining the final weight of the plane. Lighter engines permit the movement of flight batteries and radio components for the throttle to be placed more forward, helping to keep finished weights lower.

If this is your first foray into giant scale, AND your first attempt at a high performance biplane (outside of an Ultimate), may i suggest that you have someone assist you in your first few flights who has extensive experience in both areas. This is not meant to be insulting or derogatory in any manner, but the Pitts and Christen biplanes can be a handful and come to a quick end if your not ready for them.

The reason I excluded Ultimates' is because they are easier to fly than the Pitts and Christens'. They can still bite ya though.