jumpy - DO NOT get the 850 CPU. That is a PURE AM3 chip - it will fit in your MB but will not work in it at all.
Technically - per ASUS - the 955 will work with that board. Find out supported CPU's here:
http://www.asus.com/Motherboards/AMD...I_Deluxe/#CPUS
I only recommend against the 955 based on personal experience where I have seen MB's struggle with 125W chips. However, Asus makes it so they know better than I do. The 850 is NOT on that list. The 955 is so you should be fine with it.