What engine oil do you use?

Just wondering what preference/recommendations you lot have for engine oils (particularly for my 02 ZX9R). I've done a little bit of reading and found a few people using 10W40 Mobil 1, but that doesn't seem to exist in Australia (at least according to the Mobil product guide I was checking out today).
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.
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.