I have the am2 version of both cpus and they are very weak and need a decent board along with the best ram you can get in order to max them out. I am waiting on a new cpu so I can't wait to ditch the one I got.
Jon- make sure you get either an Athlon II or Phenom II. DO NOT get a regular Phenom. But yes- I would say you are about as maxed out as you'll get with your current system- its about time for a new build as the 939 socket is pretty out of date:-)
I meant a Phenom II. I am looking at a AMD Phenom II X4 965 Black Edition Deneb 3.4GHz 4 x 512KB L2 Cache 6MB L3 Cache Socket AM3 140W with 8 Gb DDR 3 with a ASUS M4A785TD-V EVO AM3 AMD 785G HDMI ATX AMD Motherboard.