Sizing the fan

[ecommerceaustin]

I have AMD Athlon 64 x2 5000+ with AM2 socket with M2N68-LA (Narra2) Specs here

http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01080282&tmp_task=prodinfoCategory&lc=en&dlc=en&cc=us&product=3629222#N1457

I've been advised that I can go as high as the 5600+ and believe the Windsor would be the choice in lieu of the Brisbane class...thoughts?

Also, with an up grade to either of those can I still use the fan that is on my 5000+?