Gav's right here, no two ways about it, you have equal torque out of the transfer case with no differential action between the front and rear differentials, if the rears were to "spin" you would need atleast one of the front tires to "spin" also.
Specifications are there for a reason and should be followed kids! A bit off-topic here, but to satisfy your curiositites and to show how serious the specs are, here are the specs for a WA1200-3 (I tried to make it as simple as poss!):
Front to rear allowable tire radius differential (<90mm)
Rear to front allowable tire radius differential (<40mm)
Radius of new front tire (bucket emtpy): 1781mm - Ratio F/R: 1.000mm.
Radius of new front tire (full bucket): 1716mm - Total of -65mm deflection - Ratio F/R: 0.950mm.
Radius of new rear tire (bucket empty): 1781mm - Ratio F/R: 1.000mm.
Radius of new rear tire (full bucket): 1806mm - Total of +25mm deflection - Ratio F/R: 0.950mm.
Allowable tire wear:
Tread depth: 136.5mm.
Allowable tire radius wear: 116mm (85% of tread)
Tire radius at allowable tolerance: 1665mm (bucket empty)
Front (New) and Rear (Allowable wear (worn)):
Bucket empty - New front: 1781mm Allowable rear wear: 1665mm Ratio F/R: 1.070mm.
Full bucket - New front: 1716mm Allowable rear wear: 1690mm Ratio F/R: 1.015mm.
Front (New) and Rear (Allowable wear (worn)): *After loaded condition F/R are the same:
Bucket empty - New front: 1781mm Allowable rear wear: 1691mm Ratio F/R: 0.977.
Full bucket - New front: 1716mm Allowable rear wear: 1716mm Ratio F/R: 1.000mm.
When the radius differential front to rear is equal to 0.925mm (1.5 times new):
Bucket empty - Front: 1665mm Rear: 1705mm Ratio F/R: 0.977mm.
Full Bucket - Front: 1600mm Rear: 1730mm Ratio F/R: 0.925mm.
Front (Allowable wear (worn)) and Rear (New) (Usually this combination will never happen):
Empty bucket - Front: 1665mm Rear: 1781mm Ratio F/R: 0.935mm.
Full bucket - Front: 1600mm Rear: 1806mm Ratio F/R: 0.886mm.
Enjoy the block of text.
P.S. How's your loader there komatskid?