The guy who donates the oil to our Car Care Clinic (for single parents) is a firm believer in synthetic oils. Every 6 months or so, we talk oil.
I run synthetic in the mill and treat it (changes) like regular oil. I do that for heat purposes and feel it is less likely to break down. Never had a problem with Syn 3, but may change as it is priced high.
I did change to Red Line heavy in the trans and am very happy with it. Reduced noise and made it shift smoother. I still run regular H-D in the primary, but would not be afraid to put AFT in there is necessary.
My dealer tells me he has never noticed a significant different between the wear using regular oils and synthetic. He is second generation H-D owner and grew up wrenching on H-D twins.
My old H-D went 84,000 miles on Syn 3 in the mill and regular in the other 2 holes. Far as I know, it continues to purr along w/o problems. Now at 10,000 on the Limited and no problems.