Plenty run them in U4 type conditions. They are fine, grease more frequently if you are worried about itAnyone have firsthand experience running the Yukon Super Joints in snow at higher RPM's? I have a set ready to install but several buddies who looked into them decided they were concerned about the joints overheating since most snow wheeling involves higher wheel speed with rapid back and forth wheel movement.
My initial thought is 1. It's cold out so they will have more opportunity to cool and 2. If properly lubed prior to run, they should stay running smooth and cool.