I would try selling your old ram and go with a 2 x 4 gb kit of corsair, kingston, gskill, or crucial if your board supports it (check the board specs on their webpage here: http://www.gigabyte.us/products/product-page.aspx?pid=3.... Mushkin also had some good reviews at newegg. Your gigabyte board will work with most brands.
I've never noticed any difference in OCing an X4 955 on an ASUS M4A79T Deluxe using two sticks or four. Max CPU OC is the same with either configuration. Of course, every system is different, but unless you're pushing for the absolute maximum RAM OC I don't think it matters much (I wasn't).