Looking for a Value, worth the price CPU heatsink is very very difficult unless you try out yourself some of them or read someone's article who managed to install this and that.
Copper is the common material used for CPU heatsinks. It is highly conductive.
100% copper heatsink is very expensive due to the difficulties of purifying.
According to my brother, there is one more above this material which is more conductive but it is generally not used in the local computer hardware.
Copper heatsink has its' own limit. You can cool down up to a certain point. Cooling down even more require a quality fans attached everywhere in the system.
AMD 6400+ dissipates quite a lot of heat. The heatsink option i have listed at the table of contents is recommended at the moment.
The idle temperature with the ordinaly heatsink with this AMD 6400+ should be around 34C average and the highest temperature is 55C average. If the heat rise to 65C and over, you should consider changing your heatsink as soon as possible. Anything below this temperature is welcomed. (of course!!)
The current heatsink in E521 won't do any jobs for AMD 6400+ unless you upgrade it.