We would need to know which motherboard you have to determine which CPUs it supports. Older AMD boards don't support all of the newer AMD processors. We also need to know what you do with your computer. Some software benefits from having more than 4 cores, but most software doesn't. For gaming the best AMD CPU is on of the Phenom II X4 900 series Black Editions. These are getting hard to find now as AMD has discontinued them in favour of their FX CPUs, which have been poorly received due to their poor performance in applications that can only use 1 or 2 cores. If you use software that supports more than 4 cores, something like the Phenom II X6 or the "8 core" FX CPUs may be more beneficial to you.