Try ASUS M4A79XTD EVO. Price match it and it's great for price. Also, 870 chipset doesn't support Crossfire (8x-8x) either; M4A79XTD EVO does. It may be slightly more optimal than 16x-4x; the M4A79XTD EVO also comes with a quality 8+2 heat sinked VRM.
All I want to assure with this setup is that I can play any of the newer games at 1080P on my big screen TV. In a year or two or three, once I can't play any of the newer games at 1080P, I would like to buy another 6950 video card and set it up as cross fire. In this way I won’t need to buy more RAM, change the CPU or even change the video card… I can just pop in another 6950 and keep playing without to much hassle or $$$$.
How much watts would I need to supply two of these 6950 Video cards?