I wouldn't be overclocking on the pro3 for more than 700 mhz on good air cooling
Also the gap between the gfx card and the cpu is quite a bit.
I suggest you bring your computer parts en-par so:
And since your monitor can do 1600x1200, a 6950 if money allows it or 6870 if it doesn't
The rest of your build looks good though for some casual gaming ^_^. You could buy a new hard drive since you're upgrading everything else if only to use your old components in a backup system. Of course, if that segate is enough space for you and you don't need a secondary machine (I have like 3 cuz i iz hardware addict/packrat) then it's fine ^_^