I'll be looking at some of the other issues... however the answer to what size to use is simple.
Whatever the user wants.
:-)
The specific size is first drawn from the theme. The specific "dynamic" size we pick is further affected by an option.
So, one of the things I do in testing things is switch to the "large print" theme. This pops sizes up very much.
"Whatever the user wants", ok! But we need to have various size for the same icons: 16x16 and 22x22.
It's important if we want nice and crisp icons in the menu and for the toolbars at the same time! I'm working on the problem for a new set of icons but it can be good if a real coder can take a look at it... 2 icons instead of 1 for each element should do trick --> "draw_calligraphic" whould become "draw_calligraphic_16x16" and "draw_calligraphic_22x22". 2 differents icons for 2 differents rendering res...
I've also submit a bug report about this different size icons problem for the toolbars between system (windows vs linux): n° [1568475] Please, take a look and tell me what do you think.
Ronan