I would just wait until either amd or guild war update for better amd cpu support. I have a 550be and a Ati 5750 and I'm also getting the same frame rate 20-30 and 8-12 fps during combat in wvw. While Intel with similar graphic and CPU power will get much higher fps.
If you want a new cpu i'd recommend the AMD Phenom II X4 965 Black Edition. You don't really need more then 4 cores for gaming.