You can run in 4x4 High on the rain without any problems. Because the 4x4 system is true 4x4 (and not AWD) it splits power 50/50 between the front and rear drive shafts. As such torque wind up will exist between the front & rear axles proportional to the disparity between tire sizes (the greater the disparity in tires the greater the torque wind up). When the torque wind up exceeds a tire's traction the tire will break free
of the surface and spin releasing the pent up force.. Wet roads have alot less traction than dry roads and the release of torque is barely noticeable. On dry pavement however traction is so high that it could easily exceed the strength of a HUB, or U-joint and cause it to explode before the tire is able to break free..
For example: If the front and rear tires only differ in diameter by half a millimeter (0.5mm) the difference in circumference would be 1.57mm. As such for each revolution of the drive shaft the rear tires will try to move 1.57mm more than the fronts.
The circumference:
Rear = 75mm x 3.14 = 235.5mm (circumference)
Front = 74.5mm x 3.14 = 233.93mm (circumference)
Difference = 1.57mm
For each 1/2 mile (804,672mm) of travel the tires need to slip 22.9 revolutions to release the torque wind up.
Rear tire revolutions = 804,672mm/235.50mm = 3,416.9 revolutions.
Front tire revolutions = 804,672mm/233.93mm= 3,439.8 revolutions
difference = 22.9 revolutions