I don't think the 120 would be the best engine for the synergy. The power with the 110 is quite awesome, and it would still be exceptional with the 91 I think.

I think the extra weight of the 120 would be very detrimental to the plane, and you'd also have to put weight in the tail as it would be too nose heavy otherwise. It doesn't need the extra power either so I would be hesitant to use the 120.