I enjoyed your post and thought I would add a few things.
I have 4 Kohler toilets with Sloan valves in my house. In 8 years only one has need any part and Sloan sent it to me for free. The only disadvantage to the toilets with Sloan valves is noise but the latest Gerbers installed in my parent's house are much quieter than my Kohlers and would not bother anyone. I don't know if newer Kohlers are quieter.
A great unspoken advantage to these valves is that they detect back pressure and overflows are just about impossible. Plug the toilet and they stop flushing instantly. Let the water do a little dissolving and flush as many times as you want until it goes down with zero risk of overflow.
Finally, when we first moved into the house one of the 4 toilets worked erratically. Sloan sent us every replacement part imaginable and Kohler finally decided to replace the bowl. When we went to the distributor to pick up the new bowl I noticed that the washer between the tank and bowl were different than the one I had. Apparently the plumber has lost the original washer and replaced it with another which wasted several days of my life and many parts from Sloan and Kohler.