The plastic bearing cage warning has come up before but I recall it applies only to the 5-speed.
The 6-speed comes with synthetic ( at least the 2000 Sport did). It only holds 850 ml so you'd have to be really cheap to want to save three or four dollars.
Although, with what you saved on oil over the life of your Guzzi you could buy a bottle of Laphroig, and invite a friend over to help you tear down your gearbox.