I run E.I. in my bike and quads but haven't switched over to it in the RZR yet. My YZ426 and YFZ450 always run warm in the dunes so it made sense. My RZR never seems to get hot and the fan rarely comes on so I'm not sure if its needed.
When I did the big bore, I went a head and switched to engine ice. I' don't know how much of a difference it makes though. I'm thinking this winter I'll upgrade my radiator. I figured the ice should be fine for freezing, cause my garage doesn't get that cold during winter.
I run straight Engine Ice....I have a temp gauge and I don't usually see the temp past the 200 mark. It's not very often I hear my fan run compared to regular coolant. I also have the Polaris Hood Scoop hood, so that also helps the airflow. IMHO, it works very good.