Get the Brisbane. Its 65nm, so check to make sure that board will support it. Looks like that board uses some kind of wierd propietary cooling also, so that leans even more towards the 65nm Brisbane since you more than likely wont be able to put a stronger cooler on.
On second thought, those chips are socket AM2. I think your current board is 939.
I found this http://browse.geekbench.ca/geekbench2/view/82548
under the search. This person is using a 5200+ X2 on the same exact motherboard as you have. So this is a plus in the "it will work" notch. Ill try to dig up some more stuff for you.
**EDIT** Scratch that above statement, the board is AM2. Youre good to go I believe. Also, the boards chipset is 6150, not nForce 4.