edit : should have paid more attn go with the GA-M57SLI-S4 since you've already got the video card but take a look at the board i linked too it's sale with a deal on amd processor purchase
i just upgraded to a 6000 on this http://www.newegg.com/Product/Product.aspx?Item=N82E168...
but i put my old x2 3800 on the GA-M57SLI-S4 for mom and wouldn't hesitate to recommend it. i not a fan of on board video but if you decide go that way find one of the nforce 5 motherboards with it and a pcie 16x slot (520's i think)
six one way or a half dozen the other. i prefer gigabyte over the asus but you won't really go wrong either way. the asus may overclock a little better but there isn't much room for that with the 6000 anyway. good luck with your build