The main difference is the engines. The 5075M has a 5 cylinder 3.0 liter turbo diesel. It does not have wet sleeves they are cast in the block. The 5085M has a 4 cylinder 4.5 liter turbo diesel. It has the wet sleeves, individual replaceable cylinder liners. This model is 10HP more. There are other versions of the 4.5 liter diesel pushing out a lot more HP. It's 50% larger displacement engine, 4.5L vs 3.0L.
The 5085M has approximately 4 gallon per minute higher hydraulic pump volume. Cab version will hold 6 gallons more fuel and weigh about 600lbs more than the 5075M.
You can get the same transmissions and hydraulic valves on both.