The following oils turn in great UOAs.
Conventional 20/50 HD 360
Any Valvoline 20/50 motorcycle oil or VR1. (Conventional or syn)
Amsoil 20/50
(im sure there are others)
I am keeping a log and oil receipts in case of warranty work on my 14 Road King.
I did my first oil change at 1000 miles with conventional HD360 20/50. Its a proven good oil in the UOAs and you will be splitting hairs to beat it..
Im trying to stay with what is oil required in the owners manual in case of engine failure I will have receipts and records. Being I am in a warmer climate I will always use 20/50 though HD says you can also use a 15/40/ 10/40 but they are a lessor choice. I always use 20/50 in my bikes, at times 15/40 in the winter..
The conventional HD 360 20/50 is a rock solid oil and proven time and again.
IF you want to use a synthetic (and concerned about staying in Harleys guidelines) I would chose Amsoil ARO Synthetic 20/50 oil as it meets the Harley condition for the heavy duty diesel rating of CH-4 and better, so with Amsoil showing this oil is rated API CI-4 Plus, CH-4 you know you are covered as using an HD recommended oil grade. its the only 20/50 oil I know with that diesel rating.
If your not concerned with having that recommended diesel rating then the VR1 is one heck of an oil to beat for the price. I would take it or even regular Valvoline motorcycle oil over the Castrol any day, that goes for conventional or syn.
This is the Amsoil I am talking about, I just wish it was easier to buy ...
Amsoil 20/50 Diesel Rated Syn