You're right, urxvt refreshes at a maximum of 60Hz (line 1021 in http://cvs.schmorp.de/rxvt-unicode/src/command.C?view=markup). Above, I mistakenly measured only urxvt. Rxvt does a select() with a timeout of 5ms before redrawing (lines 1600 and 1664 in "src/command.c"). The total latency with rxvt is about 5.7ms.