I am curious why you would need > 400 Mhz RAMDAC. I mean hell the only time I ever used 400 Mhz ramdac was to run 2560x1920@63 Hz on a CRT. And even @ 400 Mhz stuff starts getting a little fuzzy at that bandwidth amount.
What display would possibly take > 400 Mhz pixel clock over VGA?
Everything looks sharper.
I would think that the dot pitch of the monitor would start to make that a losing battle, unfortunately. My Sony G520 is the same basic specs as yours (21", 0.24mm aperture grill) and you can start to see some hint of fuzziness at 1600x1200.
But hey, nothing wrong with experimenting. Just don't try to sell that monitor here .