Hmm, I just noticed your board only supports 95w. That is a problem then the 945 is as high as you could go. But, I'd wait and buy a new AM3+ board and new RAM, then upgrade the CPU. Something is always going to be bottlenecked anyway so it might as well let it be your GPU for the time being.
, I kind of expected such a reply... What about Athlon 640 X4?