When most compare 2 strokes to 4 strokes they already know that there is a displacement difference. It's just common ground in this hobby. That is why your able to swing a larger prop and get more torque, not necessarily power, from the 4 strokers but even with the larger displacement the 4 strokers are as light or lighter in weight compared to the 2 strokes. As for the sound I don't care about realistic sounds but I do prefer the much quieter sounds of the 4 strokes. As for swinging a prop faster that doesn't mean it's better.

Look at it this way, 4 strokers produce the most power at low-mid rpms with alot of torque while 2 strokers produce the most power at high rpms with very little torque.

Now as for same displacements swinging larger props here is what I pulled from the OS and Saito websites:

OS91 (2 stroke) recommended props: 13x8-9
Saito 91 (4 stroke) recommended props: 12 x 8 - 15 x 6


I guess it all boils down to personal preferences, the needs of the airplane in comparison to how you want it to perform and of course your spending budget.

If I'm building a Morris profile that I want to 3D the hell out of then I go with a Saito 72. If I were building a Diamond Dust that I wanted to push 200+ mph I would indeed use a 2 stroke.