Ozone,
You were pretty close there on the Amsoil site. Here is the white paper on motorcycle oils. They do both 40 and 50 weight separately. All the industry standard test procedures are referenced and listed at the end of the paper.
AMSOIL - A Study of Motorcycle Oils
I turn my own wrenches on my bikes since I have had questionable work done by or advice from a number of HD dealerships here in the Houston area. Turn over is pretty high at these places, and I hate to have my bike be an OJT project for some newbie. Now if you have a dealership or non HD bike shop where you know the mechanics and can find out about their history and experience, great. Stick with them if you don't want to do it yourself. Otherwise, you are taking your $18k+ asset in to someone you don't know and gambling on their ability.
On fluids, I have been MOST impressed with Spectro Heavy Duty Platinum 6-speed Transmission Oil in the gearbox.
I bought my bike with about 30k miles on it all on SYN3 changing every 2500 miles or so. Very shortly thereafter, the cam chain tensioner crapped out. Switched to Mob1 VTwin all around. Then did some research and switched to Mob1 VTwin in the engine, Royal Purple 75W140 heavy duty gear oil in the tranny, and Spectro Heavy Duty Primary Chaincase Oil in the primary (obviously!). That was only while I was waiting for the Spectro Heavy Duty Platinum 6-speed Transmission Oil to come in. After putting this stuff in the 6-speed, there is NO comparison. My transmission shifts very smoothly with an almost inaudible sound or feel on each gear change - up and down.
In my little bike ('91 Dyna), I used all HD fluids. Their standard HD engine oil, primary oil, and transmission oil. The gearbox on that bike is now shot (67k miles). The engine consumes oil at a higher rate than I think it should. The primary fluid is always VERY black when I change it at about 10k mile intervals or when something happens. This bike is now parked in my garage waiting for me to get my round tuit so I can rebuild it. So, the HD logo on a package is just that - a logo. It is not a guarantee.
Just my humble opinion based on my own personal experience.
TQ