I normally have mine set above 75 Hz, althought I've never ever seen flicker on any CRT screen that I can recall...
For a couple years I had an old 17" IBM monitor with .27 dot pitch, and had it set at 1024x768 @ 60 Hz. Never did notice any flickers. You can call me weird if you want to, but for some reason I've never had any problem with that and/or eye strain.
I'm on a dual setup now though 21" with 1600x1200 @ 85 Hz. You may think that 85 Hz is overkill, and it might be. But I looked at the screen and desktop at 70, 72, & 75 Hz. And couldn't really notice a difference at the different rates, until I took it to 85 Hz. Then it was like "Wow!!" There was a whole 'depth' that it added. Not sure why, I I haven't noticed it on other monitors, but it definitely added a nice touch on gaming, you know having a pseudo-3D look to it. The colors and contrast were just so much more dynamic with it set at 85 Hz. If you know, then please do tell...
Anyway, I'm running it on Sony Trinitron tubes... gotta love 'em...
David