4x4 ASCII Font (2016)
This is smaller than I've ventured to go; I used 4×6 in http://canonical.org/~kragen/sw/dofonts-1k.html (and I think the font is Janne Kujala's design; I wouldn't be surprised if I changed a few things, but it's been more than ten years, so I don't remember) and a proportional font that averaged 3.6×6 in http://canonical.org/~kragen/sw/netbook-misc-devel/6-pixel-1..., used by http://canonical.org/~kragen/sw/netbook-misc-devel/propfontr... to render http://canonical.org/~kragen/bible-columns.4×6 is 24 pixels, which is one pixel less than 5×5.If you're rendering a single column of characters, I think you can do 3×n, where n ranges up to 7 or 8 but is usually more like 5: http://canonical.org/~kragen/sw/netbook-misc-devel/3xnfont.All of these are larger than 4×4.My hat is off to the Simplifier.