I did a lot of research on oils around the year 2000 (and yes, a lot might have changed since then, but this is food for thought) and it was interesting to read that back then, the only two oils on the market that were actually "fully synthetic" were AMSOIL and Mobil 1. By fully synthetic, I mean that they were made in a test tube, and not by refining mineral based crude oil and adding synthetic additives. There may be other manufacturers now making real fully synthetic oils, but this is not the point.
This position may have changes over the last 12 years, but there was an interesting test they did on control engines on dynos (road bike engines), and checking the polymer length of the oil at the recommended service intervals (I think they used ZZR1100 engines from memory). The results were that at the 6000km service, both AMSOIL and Mobil 1 had 93% (ish) of the polymer lenghts the same as they were when the oil went in the engine. Other brands were down to as low as 40%. I must try to find that report somewhere.
However, the point is that AT THAT stage, both AMSOIL and Mobil 1 out performed the other oils on the market.
I used to run Mobil 1 in my ZX9 and with 100,000km of thrashing, it was still in spec on the compression tests, burned no oil between the 6000km services and still went like a cut snake. I couldn't get AMSOIL in the town I lived in, so this was the best that I could do.
IMO: Have a good read on the net, and with the top end quality oils, you usually can't go too wrong, however, some are better than others.
Interestingly, some guys will go and blow $100 on a night out on alcohol, but won't spend the same amount on 4 oil changes.
