What's the ideal icon size?

[Megalith]

I thought it shouldn't matter, but the custom icons I have set for some of my toolbar icons look extremely jagged.

[highend]

24 x 24

This tweak (if set) can influence the look:

v15.20.0202 - 2015-05-26 13:24
+ Toolbar: Added a tweak to zoom the whole main toolbar by a factor between
0.5 and 8. For example, this would double the size:
ToolbarZoom=2
Note that the stretched native toolbar graphics will be rendered pixely.
There is no smoothing available here. Custom Toolbar Buttons, OTOH, using
the new option to employ larger PNGs etc will look great.
If you like to push big things, try this:
ToolbarZoom=8