It's interesting to see all the different stuff folks put in a Harley with good results. The conversation is almost always: "I put (insert brand) into my bike, its amazing. A lot better than (insert brand). Really quieted down the valves and made the transmission shift better with less clunk". Helps to insert the following acronyms and phrases: HDEO, Zinc, PCMO, additave package, OCI, detergent, OPE, and make up a few more for good measure: You don't really need to know ANYTHING about any of them. Leads me to believe that you could run about anything but baby oil in a V-Twin with good results. The twin cam is a GREAT engine and doesn't really care what you put in it. I bought my 2010 FLHTK "Grandpa Glide" new and have about 35k miles on it. Amsoil MCV 20w50 for the engine once a year regardless of mileage. Trans has the 75w-110 gear oil in it and I doubt I'll change that for a good many years. Primary... Well. That's where I experiment. I've run Rotella 15w40 and T6, Amsoil MCV and MCF, and my latest favorite: ATF. The ONLY one I could tell a lick of difference was Formula+. It felt worse to me.
Some of the old farts put Rotella 15w40 in their contraptions for decades without issue. HD engines are separate from the transmission so you can run just about any 50w oil with zero problems.