Nice one, i should have read on a little! the 75w80 seems to be more conventional, used for everyday applications. There isnt a massive list of benefits...
"■Ideal for manual transmissions that are designed for maximum fuel economy."
The 75w90 is for motorsport/highly modified vehicles, Huge list of benefits...
"■Exceptional cold flow properties for easier gear changes.
■Fast lubrication flow to component extremes on start up
■Very good oxidation resistance and superior thermal stability. Low friction/ low drag formulation to help reduce operating temperatures.
■High film strength for maximum component protection. Significantly reduces friction, temperature, wear and minimises power loss."
The "90" is twice the price, give or take, but sounds like it may be good for a box prone to failiure. Anyone used this stuff yet?
Is the difference between 80 and 90 liable to cause its own issues?
I read that additives in these oils can break down over time, causing sludgy build up, and less effective operation in extremes of temperature.
I suppose a competition oil would be changed frequently, thus negating above issues.
Sorry, getting waaay too involved now!

Its just that it would suck paying twice as much for something that lasts half as long!