Well.......
I ran the Pro-motion on my last Pro 163 with an X3. I had some miles on it as stock before I made the switch. This sled also had a narrow front end (37"). Now did it make a difference, yes it changed the handling on that sled and it was noticeable. Was it a game changer......no. Personally I thought it helped the deeper lug X3 not want to pull that straight line. Not that the 3" track just wants to go straight but there is a difference with this track. After adding the Pro-motion and the narrow front end, the sled was extremely quick in reacting to rider input!!! I also found myself going into the "wrong foot forward" position less. Now I still had to go into that position but it just seemed less than before. It made the sled more "twitchy" if that makes sense?
Side hilling, I didn't see a ton of difference there but it did take a way a little bit of the stability. It wasn't a bunch but you could feel the sled move around a bit more under you while you traversed a side hill, and the rider input changed. Not bad, just different and again it reacts to input faster, whether its you or the terrain beneath you.
Now.....onto the Axys, that I currently run. 163 / 2.6 and a K-Mod 37" front end. Does this sled have the Pro-motion.......nope.
After riding the Axys with this setup, I haven't observed or felt the need to add Pro-motion. The Axys side hills awesome, is stable and reacts to rider input appropriately. I "think" by adding Pro-motion to an Axys, may make it overly "twitchy" or too fast if that makes sense??? I also think that if you are a heavier rider, you will probably notice more by adding Pro-motion verses a lighter rider. Basically no different then a heavy dude taking a step back on the running board for input vs. the light dude taking a step back. The lighter dude is going to have to step further back for the same sled response.
Hopefully that makes sense and again, this was my personnel thoughts based on my set up and the conditions I ran that sled in during those rides.