Read the thread more carefully the debate is about what Ford specified in the owner's manual - not about the relative viscosities of different oils. The manual clearly specifies SAE 80 for all three sumps.
Now than - about that school thing:
I said most UTF's have the same viscosity as SAE 80 gear oil. You don't need a viscosity plot to determine that - the gear oil viscosity grades are all specified at 100C by SAE J306. The manufacturers product data sheet for any given UTF will also provide the viscosity of that specific oil at 100C. I provided the J306 numbers alongside the CNH Ambra Multi-G 134D specification in my initial post. Go back and look - the Ambra is dead smack in the middle of the viscosity range for SAE 80 gear oil.
The viscosity of hydraulic oil is not graded at 100C. Hydraulic oil grades are specified by ISO not SAE in DIN 51512 and the ISO grade number is the actual viscosity (+/- 10%)measured at 40C. The allowable viscosity range of ISO 46 hydraulic oil is 41.4 to 50.6 cSt @ 40C. Per Viscosity Oil, the manufacturer of Ambra 134D, it has a viscosity of 60 cSt @ 40C making it very close to an ISO 68 (61.2 to 74.8) hydraulic oil. It actually falls just short of the minimum but if you really must make a comparison it would be closer to an ISO 68 oil.
Conventional hydraulic and gear oils have very low viscosity indexes - something around 100 - making them poorly suited for both winter and summer use in anything other than very temperate zones. UTF's on the other hand have very high viscosity indexes - typically 135+ - making them excellent all season lubricants. That is why UTF was developed - as an all season multi-purpose replacement for conventional gear AND hydraulic oils. Their additive packages are tailored to that dual purpose role and they typically meet or exceed the performance of conventional oils in either application