NJD:

In two-strokes, I have a slightly smaller twin that maxes right at 100 mphg with a pair of Magnum .46 engines, on 10x8 three blade props. And a slightly larger twin with K&B .61 engines and 12x8 three blade props, similar speed.

While I have several twins, none are running 4-stroke engines. As a rule of thumb, though, divide the 2-stroke size by 0.6 to get the equivalent power in a 4-stroke. But don't forget the weight penalty with the 4-strokers, and your density altitude.

With all this in mind, I'd say the .91 engines were preferred, don't really think they will be that much heavier than the .80 engines.

Servos? For normal flying standard servos work very well on that plane.

But do watch the weight. At 12 pounds it will have to be pretty fast, which you wanted, or it will be a pig. Another reason for the bigger engines. And 12x8 three blade props.

Have a good time, build it your way.
. But power gets it off the runway.

Bill.