When I still had my 07' 650 classic, I used 87 or 89. I'd use 91 maybe once a month without any issues. Now I didn't ride daily as a commuter, but I'd put quite a few miles on her monthly. As far as maintenance, changing oil, etc, I bought a Clymer service manual off eBay and followed Yamahas recommendations for all of that. I changed the rear end fluid according to factory specs as well, that's something you don't want to overlook. Hope this helps.