Mule 4010 is 617cc governed around 25 mph. If you think it is a dog, then I would be inclined to get a 700 or up Ranger.
For what it's worth, I have never felt my Mule is underpowered, just slow... two different things. I wish it did not have a governor on it.
If you really want to go, look at the Razr crew.
I have only rode in that one mule and only two times and it really is a dog. We would get stuck left and right because it did not have enough power. I think it was the base model mule and an older one too 2-3 yrs but it really was almost worthless unless it was dry ground and not too steep. I was not say that they (mules) are all like that because I have only been around that one. I am just a Polaris guy from way back and I have always had great luck with them so that is why I am looking there first. I would love to get out and hunt with some of yall that have the different UTV's and get to know them for myself. Thanks for your opinions guys keep them coming.