60Hz convolved with 85Hz would give beat frequencies at @25Hz and 145Hz. Obviously the 145Hz wont be an issue, but the 25Hz might be noticeable. As the refresh rate is reduced towards 60Hz, that 25Hz figure drops.
The limit of the human eyes ability to percieve flickering is generally acknowledged to be between 20Hz and 30Hz. PAL televisions use 60Hz interlaced, ie each scanline is changed at 30Hz, whilst NTSC sets use 50Hz (ie each scanline at 25Hz), so from that, most people should be ok with a 85Hz refresh rate.
(But televisions give some people migraines and eye-strain anyway)