80W90 is better stuff than the EP80 or EP90 of old. I have just spoken to Castrol and they say it is a change of oil formulation which give a cold temp viscosity of an EP80 and a warm temp viscosity of an EP90, in the same way as a 20W50 engile oil has two viscosities measured.
It is possible that an EP80W90 if left in the vehicle for extended periods (unlikely in a landy) that oil degredation of an ep80w90 will be marginally worse than an ep90 - it will tend to get more like an EP80 when it degrades.
They also stated a couple of interesting points.......
Certain oils are now GL4/GL5 compatible and can therefore be used in gearboxes, unlike straight GL5's.
On units (T-boxes/gearboxes/axles) that suffer some abuse, it might be worth considering an EP80w140 oil as this gives more of a cushioning effect betwen gears. They recomend their Safx-J EP75/140, but said it is considerably more expensive,that is, however, offset against extended oil change periods (prospectively twice the change interval).
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