I have been using Yamalube 4R 20-50 semi-synthetic for a few months now. It has really made a difference in the way my 660 shifts. I have not noticed any difference in shifting on my 700 but it does seem to run smoother. I am sure most of that is in my crazy mind though.
In the drag Raptor I used 2qts of yamalube and topped off with lucas oil stabilizer.....in the 700 I'm going to use bel ray thumper semi sythentic oil(2qts) and if I have to top off for full I'm going to again use the lucas oil stabilizer.
I use yamalube 20/40. I have been told to stay away from full synthetics until motor has about 75 hours or so on it, seems they think the synthetic is too slick to seat the bearings and rings etc. Whatever oil you run should be a motor cycle oil they have the additives to make the wet clutch live longer and function properly. Although I have had friends that ran regular car oil with no trouble, just not recommended.