I sit in front of my box at work at 85Hz and at home, my screen is at 85hz. When I used to have 75hz at work, I had numerous headaches, but now its gone since I lowered my resolution a bit to get back 85hz. At home, I run 1600x1200 at 85Hz and its quite pleasant to look at. My friend says he's happy at 60hz, but I simply can't stand it.
Your mileage my vary.
Also, I like playing games at 1027x768, I get 120Hz on my monitor for that.
vash