Is there a big difference between the various weights? I don't have the service manual for my bike, but the older one hosted here suggests 10W-40, 20W-40 and 20W-50 are ok for the B model 9R. Not too sure which synth one I want to use.

EDIT: ok, so I found 10W-40 Mobil 1 is actually "Mobil 1 Racing 4T 10W-40". So where the hell (south of Melb) do you get this stuff? My locals don't seem to have it.