With either engine, you will need to try different props which one works for the kind of flying you want to do. For example, I am using the OS FS 91SII on a Reactor 46 3D and a 14x6 MAS. I tried the 15x6 and 15x4 props and the engine would scream and the airplane wouldnt have any traction. I tried a 14x4 APC and the airplane wouldnt hover. I compromised to the 14x6 and if the engine is setup properly, I find it to be the best compromise.

Bipes are very draggy airframes, so I would err on a larger prop. Depending on which make and type you use your results will be different. If you have RF, you could try the Skybolt in it with the FS91 and different size props and use that as a startpoint

Ameyam