Losing image quality is somewhat the same as saying losing the performance, and vice versa, isn't it?
As i said, you wont notice the difference!
Loosing performance is lower FPS in games / lower bench scores / smaller overclocking gains.
Loosing image quality effects brightness, HD video, 2D/3D windows applications, graphics designing (i assume).
Either way I'm hoping to get a new Sumsung 24" early in the new year so i guess ill find out for myself what the diff is...