Oils like MTl 80wt does not have the viscosity of a true 80 wt like hypoid 80wt gearbox oil.  If it did your clutch would probably slip until the oil temperature was well over 200 F deg.  Two stroke transmissions seldom exceed 180 degrees even after long periods of hard riding

1.  Our two stroke transmissions would have the longest gear life if we used the 90 wt to 140 wt hypoid transmission/differential oil but would also pay a high price in power loss with the transmission and clutch basket "churning" the thick oil.

2.  Our multi-disk wet clutches  would have the longest life and torque transmitting ability if they ran something like a 2 wt oil, but gear life would suffer.

The engineers at the major manufactures are aware of the two above facts and have found the best compromise of clutch life, gear life, clutch slippage and power loss is using one of the readily available thin multigrade engine oils but changing it frequently. 

I think that marketing departments of the oil companies have created the "special oils for engines/transmissions" to have a reason to charge outrageously high prices for these "speciality oils" and to pacify the environmentalist that do not want us to ever change our oil so that we do not consume oil.  The marketing departments of the major offroad manufactures are also becoming increasingly aware of the influence the environmentalist are having on the legislation and the power they have in closing down riding areas.

Honda has some of the best engineers and product testing programs on the planet.  I do not think that they subscribe to the oil industries claims that they have special oils that will last for long periods of time in engines that share the same oil in the engine and gear box.  If their testing proved that these speciality oils did what they claimed they would not be designing some of their racing engines that use two separate oil systems.  One for the gear box and one for the engine oil. 

Engines and transmissions that run under extreme load conditions need frequent oil changes regardless of the quality or cost of the oil. 

I do not recall what Suzuki says to run in their LT two stroke transmissions but most engineering departments of the manufactures say to run 10w30 or 10w40 motor oil.  I think that the marketing/public relations departments have the final say so when it comes to what is published in the owners and shop manuals.

Think about what you read in your shop manuals............ is it from the engineering department or the public relations department?