I wouldn't even bother. That board will only run at x4 in the 2nd slot and there are only a few games that ACTUALLY take advantage of Physx. Not to me mistaken with Physics. I wouldn't worry about it. It will just suck power and from what I gather it can actually rob a frame or two when it sits idle.
PS. if you want a performance boost you can turn on the Advanced Clock Calibration on in your Asus bios. This will unlock the other 2 cores in your 550BE. My buddy JUST did this to one of his PC's and worked like a champ. The x2 and x3 Phenom II's are all quad cores with 1 or 2 cores disabled. At the beginning they would use chips that had bad cores, but their fab process has gotten so good that most of these chips have 4 working cores. Check out this link on the 555BE which is the same for the 550. And welcome the 2 new cores to your family.http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=3730