What parts to use....

Ok, so I upgrade my monitor to a dell 2405 fpw which supports up to 1920x1200, and notice that all of a sudden my old faithful system (p4 2.8, 2 gigs ram, geforce 6800, IS7 board) all water cooled, won't do all I need it to anymore; or rather the 6800 won't support the dual link DVI to be able to run at full 1920x1200.

Now I know I'm being picky, but I'd REALLY like to be able to run that res without getting rid of all my components, or at least without shelling out another 1-2 thousand dollars to upgrade my computer completely. So I need some recommendations of build outs for a cheap upgrade which can run dual link dvi. I'm currently considering the ASRock P4VM890 (a company I've never heard of before, anyone have any good/bad experiences with them or their products) that way I can keep my cpu and ram, then getting a used geforce 8600 or something which I can overclock (why buy new when you are just going to void the warantee when you get it by installing a new block) still not sure what GPU water block I'll use or anything like that.

I'd like to keep the new buildout at $500 or less and get the best components I can for the price knowing that I'm going to overclock most of it (I already overclock my processor and gpu, and my ram best I can). What do you guys think?

Thanks for any and all replys.