If you
trawl back through the Hexus reviews you'll find that an X1650, which roughly equates to an X800 performancewise, performs as well as, or better than, an HD2600. An 8600GT (= 9500GT) is generally just about ahead of the X1650 - but its all very dependant on the game title and IQ settings you're running.
The HD4200 lags significantly behind an HD3450, which has identical performance to an HD2400. So the integrated graphics on a 780G / 785G and even 790GX board would be a significant performance drop against an X800 (although they would obviously have the necessary featureset (DX9c) to play the games the OP is struggling with). A cheap AM2+ board and 4650, at ~ £75 total, would be a much better investment,
tbh...
How do I now all this? I've been pondering an upgrade to my 9800 Pro for a while now, and I wanted to know where all of the different models stood in relation ot each other