I've been frustrated with font sizes when I print documents and playing games with zoom level, etc. But it turns out Firefox has a good, general solution: no more playing around.
Firefox allows one to set minimum print font size. In limited testing, it works well, as it should, since the browser should be able to re-flow text for changing font sizes. Other browsers probably have some similar mechanism, but this is for Firefox:
Preferences | Content | Fonts&Colors | Advanced | Minimum Font Size
I set mine to 11. It does sometimes use more paper, but several times I've seen a printout, and tossed it directly into recycling and tried again.