I was looking for a new sled and was wondering....What is the difference between the Pro X, the Pro XR, and the Pro X2?

Prox has ryde shocks and a 1" track for 2004 , prox 2 has walker evans shocks and a 1.25" track and a short race style seat that is a POS , and a XR is a rider forward more of a stand up race sled with a short seat with walker evans shocks and no sway bar and stiffer springs. the 2004 XR 440 motor is a time bomb , most of them only last 1000 miles.

How reliable are the Pro X 800 motors?

99% of them are trouble free for 5000 miles with zero issues related to cranks but there are a few , More of them have had exhaust valve problems . This is the reason for polaris changeing the metals that the valves have been made of , again updated valves are much better.

Be prepared to put a little time and money into it though to make it perform to it's potential. Make sure motor mounts are in good shape(easy to replace if they're not), buy the torque and push arm from SLP as well. Some clutching goes a long ways in these sleds too.