Take of yer beer goggles, mate! Just kidding...
Do you run your brightness super low or super high? Usually brightness pays a factor into eyestrain for me, not font sizes.
Also, I typically use Chrome on my iMac 27" and scale pages at 125% and set minimum font size to 12, 13 or 14. Did you try that?
You can do this within Chrome or by extension? If so which one?