If an oil has a JASO-MA grade, its best for motorbikes, doesn't matter what API rating it has. But since few oils available in Pakistan have JASO ratings, we have to stick with API SG rating.
Motorbikes use only one oil to do all different types of lubrication and other stuff for which cars use two or three different oils and water cooling.
I have to change Caltex Havoline oil in my motorbike after only 1,000 kms., but people using it in their cars change it after 3,000 kms. The reasons: 1) in cars the oil is not supposed to work as a coolant, 2) in cars the engines run at a lower rpm than a general 9,000 to 10,000 rpm of a motorbike engine, 3) in cars the engine oil is not subjected to extreme stress of gearbox lubrication, the gearbox in cars is separate and it uses gearbox oil, and 4) in cars the slipperier the oil the better is the fuel consumption, as the clutch plates are not submerged in the oil, in motorbikes however, the clutch is submerged in oil and will slip a lot earlier if a new car oil is used.
If an oil is good for motorbikes they should get a JASO-MA rating and the issue will be settled. The 'SILKOLENE OIL PRO 4 15W-50' oil mentioned above has multiple ratings: JASO MA & MA2
API SG, SH & SJ
I think a version of Total Quartz has SL and SG ratings (don't remember the number).