firo40 :
That depends on what motherboard you're using
This is everything it supports
https://www.asus.com/Motherboards/M4N98TD_EVO/HelpDesk_CPU/
The fastest being the Phenom II X6 1100T, I have one and it still keeps up with today's modern stuff. That said they don't make it any more but it can be found on ebay for around $100 or less these days.