I also have this problem on a Dell L502X with nVidia 540M GT. I upgraded from Windows 7 to Windows 8 and in a couple of hours I started to feel my eyes getting tired. Then I looked at another computer here at my company and noticed the difference in text.
Since then I've tried all the suggested solutions with DPI, resolution, ClearType, switching cables, different graphic drivers and nothing worked.
I reinstalled Windows 7 but 1-2 months ago I tried W8 again hoping the problem was fixed... but its was the same.
After I wrote this I decided to try W 8.1 Pro Preview Build 9431. I installed the 326.80 nvidia graphics driver and I can see a significant improvement- still not perfect but close to how it works on W7.
I've disabled for all programs scaling for high dpi