In my experience once eyestrain starts, it only gets worse.
I'd say use the 75hz setting if it pleases your eye... the monitor will run cooler too.
A couple of other suggestions...
Check the brightness (black level) set it so that you see a barely noticeable haze on black backgrounds, then turn it down until the haze just disappears. (i.e. make sure you are seeing black, but not losing darker shades of colours)
Reduce the contrast. The ideal setting is one that is just bright enough to view comfortably. (i.e. probably about 50% of full brightness)
I don't even want to guess how many monitors I've worked on where the brightness and contrast were all the way up, and all I had to do to satisfy the customer was re-adjust them.
FWIW... a 15 inch monitor displaying white at full brightness and contrast, produces about the equivalent of a 40w lightbulb... bigger monitors produce even more light.
<b>(</b>It ain't better if it don't work.<b>)</b>