I see BMW does list a synthetic gear lube as Super Synthetic. This is the only info I can find on it. "Recommended for all BMW motorcycles after 1970.
High performance synthetic provides high load carrying characteristics, minimum foaming, and exceptional resistance to thermal degradation.
Exclusive chemistry reduces internal friction and enhances power output under extreme service conditions."
Plus = stated above
Minus = does not state it is recommended or warranted for extended service interval. Likely formulated by the lowest bidder to make minimal specs. Can't find out basic info like base oils (petroleum synthetic or chemical synthetic), typical properties, MSDS. They don't compare against anyone.
Red Line 75W90 synthetic gear lube.
Plus = Lots of info at http://www.redlineoil.com/products_gearlubricants.asp
. This is a chemical synthetic (polyol ester base). "Allows extended drains in non-warranty vehicles. Redline is well known for making quality synthetic lubricants, leaning more toward racing applications and been in business since 1979. Compares against non-named competitors.
I offer a 3rd choice. Amsoil Synthetic Severe Gear 75W90 Extreme Pressure. Lots of data at www.amsoil.com
. This is a chemical synthetic (PolyAlphaOlefin). Amsoil specializes in the longest warranted extended drain intervals in and out of factory warranty since 1972. They compare their products against named competitors. They will release a "White Paper" soon, likely comparing against Red Line, BMW and many more in standard ASTM gear lube tests performed by an independent non-profit lubricant research institute. I had tried a BMW synthetic lube in my 137,000 mile K1200LT at the first change interval from the BMW factory oil. Then switched to Amsoil and noticed improved shifting. Kept it in with 24,000-36,000 mile change intervals in the transmission and final drive. No failure with the final drive, but did break a tooth in the transmission at 136,000 miles (covered by extended warranty. It looked like a manufacturing flaw). Transmission showed no wear and was spotless.
Based on the above information, my preference would be Amsoil first, Redline 2nd, BMW 3rd. If anyone has more information, please share.