Per-screen font config?

xrdb uses the C preprocessor (because of course it does), so it supports conditions. Here's a snippet from my .Xresources:

#if SCREEN_NUM == 0
Xft.dpi: 157
#endif

#if SCREEN_NUM == 1
Xft.dpi:  96
Xft.antialias: 0
#endif

Now xrdb -merge will do the right thing on each monitor, and when you log in, assuming one of the myriad X initialization scripts bothers to look at your .Xresources, it will also be set correctly.

(Note: the Arch Linux Font Configuration page has more examples, but in the interest of preserving this for posterity, I have included the relevant example above.)