We have a group of several hundred flying a pusher with Rotax engines of all three variations, 912UL, 912S and 914.
We are mainly split with Ivo and Warp Drive together with some others. A fair few have a two blader made by our aircraft manufacturer but I'd say Ivo was probably the most popular.
You might get more drive out of a medium (That's what I have) but the mini will have less inertia and that is quite critical with Rotaxs. Also you need to consider clearance. Very few of us have in flight adjustables, mostly not worth the weight and complication on a light plane with limited speed anyway. It might just make some sort of sense in particular circumstances but we set the ground adjustable for our most critical phase of flight and just accept the slight degradation of performance in all the other circumstances.