Well, and old debate! Everybody has different points of view and experiences... we need a good barbecue to talk about this matter. Imagine, down here in South America this topic will mean at least one pound of meet (each participant) accompanied with red wine... to prepare a good "asado" takes at least two hours including a football match...
Next time try a semi synthetic one API SG, JASO MA, it's the best of two worlds. Never ever an API SJ. The synthetic oil is only for RR's or other high performance engines, it will wearing out the clutch in veteran motorbikes like XT's. We discuss a lot in the argentinian XT forum, Chile, and in the brazilian one also. It's just my experiencie in motorcyles engines air cooled, no oil radiator, dry sump, wet clutch like Suzuki DR350, Honda NX650 Dominator (three of them) and my adorable XT600E, the same type of engine than yours (maybe except the dry sump, not shure). Nothing goes wrong in thousands of miles and many many journeys in different trips.
The brand I use is MOTUL 5100, 15W50 (I use to drive in hot/freezing climates like mountains & Atacama desert)
Once again, thanks to Wordreference.com