The 21" adds height to the front end (2.8"overall / 2 = 1.4" taller). So if your vertically challenged already you will have to either lower the front end or reconsider your choice.
The ride as stated already is just a tad harsher than with a 18" or 16". It stands to reason as your loosing side wall.
The contact patch, there isn't a great difference from the 120 to the stock 130. Yes it is a mind thing for sure.
Having run the 18" and the 21" the 18" IMO is a better ride and gives the feel of a more planted front end. With that said there is such a little difference once you get use to the 21" I wouldn't let that be a determining factor.
The load rating as previously noted is correct. RC Components has stopped using Metzeler's on their 21" wheels and has went to the Avon's. Avon supposedly has no issues with their 21" on a Bagger. I thought I saw another wide 21" tire the other day from, Dunlop maybe.
If I were starting with no wheels I'd consider a 19", I wouldn't change from a 18" to a 19" but I would go from a 16" to a 19".
The 21" is just plain good looking!
I would have went 23" if it would have fit without the crash bar removal, I use it and can't afford to give it up.
18"
21" chrome
21" black