what could cause such blurry text at 2560x1600?

My friend has a HP Z30i that can support 2560x1600 at 60Hz

the embedded video card is doing 1920x1200

So I first upgrade to an old Nvidia Quadrdo FX370, it supports 2560x1600 just fine, but the text is very blur

So I then switch to a Nvidia FeForece 8600GT, once again, it can do 2560x1600, but the text is blur, and when I open a small windows like the Advance setting tab under Display adapter, the text is unreadable.

So I then screen capture the text and saved in a PNG file as proof.

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I now bring back those 2 video cards w/ the same DVI cable home, and test it on another PC and connect it to an slightly older HP ZR30W, which also can run 2560x1600

The video card can display 2560x1600, and the text is crystal sharp.

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I then view those 2 capture text PNG file on my own PC, shockingly, the text is ALSO Crystal sharp, eventhough I can't see it at all on that HP Z30i

In other words, I CAN see the text very blur, but the Screen Capture Display saved PNG files shows just fine on another PC

Now, what is causing this? EDID?

Play with your refresh rate, also if you have mutable displays make sure they are both at the same refresh rate.

Any results when (re)running cleartype tuner?