I use Mobil 1 Synthetic 20/50 (V-Twin) in The Crankcase, Trans, and Primary. I have a 2008 FLHX (As you can see by my username). Living in Southern California, I've found that this works really well in my machine.
The first 10,000 miles of the machines life it had Syn 3 in it, and I noticed a lot of Trans whining in 5th and 6th Gears. With the Mobil 1, this whining sound is gone, the shifting is smooth, and the valve chatter is much less noticeable at 2500-3000 RPM.
Anyone have similar luck with the Syn 3 junk that HD pushes like crack to addicts?