Well, bit the bullet, uninstalled jbpatch and updated my touch. It seems quite snappy with all the new stuff. As the files show the fonts are still the same as 5.1.x ones. But luckily the /font and ;fc-cache still works to replace the internal Caecilia font with new ones without any file replacement on the device (verified by before-after screenshot and my eyes
).
Edit: PDF viewing and scrolling while zoomed seems to have improved a lot.