You might be disappointed in the framerate drops you'll get in newer games... I bought the Radeon equivalent of the 560, and it's definitely held back by my CPU. (Check my sig.) The weakness of an Athlon X2 is much more apparent when paired with a strong card.
Don't get me wrong, all games are playable on max settings, but you'll still drop below 30fps in many places. Minimum framerate is determined by the CPU.
You've got the right idea upgrading to a Phenom soon. A strong CPU will keep your framerate smooth. Best cure in the meantime is to never look at your framerate