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 15w-40 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 15w-40 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.