This is a big one for me too. The lack of power, acceleration, and ability to get the front end up compared to what I know it does on dirt or on a sled is a major disappointment for me.
My KTM 450 SXF with a 520 big bore and Yeti 129 pulls very hard when you are on the throttle and the track is hooking up. Maybe not dirt bike hard but I can accelerate as fast or faster than the 800 sleds that I ride with. It gives you a definite seat of the pants thrill. The 520 made a big difference in power for sure.