Watch the weight... 3D is all about keeping the plane LIGHT. If its heavy it won't do some of the maneuvers, no matter what the power. Thus... the lighter LA series may be a good option to consider.

For torque... can't beat a 4-stroke. And the .91 FS is lighter than the .61 FX, and gives more power. That's the main reason that of the listed choices.. I'd use the .91 FS. And once you try the FS... you may not want to try a 2-stroke again. They are that good.

One thing about the O.S. 4-stroke mufflers... soft metal. Easy to overtorque and strip the threads. Use Permatex "Copper" silicone High temp gasket sealant instead of the lock-nut. It won't vibrate loose and you won't strip out the threads. It breaks free easilly when you want it off.