We had an 07 800 2x that had an overheating problem. We had it back to the dealer 4x trying to get it figured out, but they weren't able to so we traded it in. Some of the things they tried: check to make sure the radiator is absolutely clear, no sticks, mud, or seeds, etc. Make sure it isn't leaking - even a pinhole leak. Check to make sure there are no air bubbles in the coolant. They checked the fan relay sensor and said it was functioning correctly. They replaced the filler neck thinking it was misshapen and causing vapor lock. They completely took apart the water pump to see if the fins were warped (they weren't). Replaced the thermostat. About the only thing they DIDN'T do was tear it apart to see if the head gasket was shot. That machine only had 1100 miles on it, and the overheating didn't start to happen until the 800 mile mark. The machine would get very hot on our legs, and then you'd start to smell coolant, and then it would start flashing. Sometimes we could go several miles before it happened, other times it happend within 3 miles. We carried antifreese with us all the time!
So I'm very curious to see if you get your overheating issue resolved, and if so, please post to let us know the source of the problem. Thanks, and good luck!