A 60 sized plane ( 2 cycle 2) with a 70 4 stroker may be "scale" but it is always nice to have extra power, especially for sticky situations that arise..

If the weight penalty was small, and price was not a big factor I would step up to a 90- (need prop clearance though-)

Don't think you would have a ton of vertical with an OS-91, bit it'd be about right-

For V E R T I C A L throw a YS-120 on it>

Best of luck!