The 7750 is cheaper and at 3.2-3.3GHz overclocked can match the E5200 @ 3.0-3.1. The thing is, the E5200 uses less power, generates less heat (especially when overclocked), and with the right board and sample is reported to have gone well beyond 3.0Ghz. On that MSI board you picked you probably won't go past 3.0Ghz with the E5200. I'm not to crazy about G31 based boards, so at least as far as motherboards go it would seem like your AMD build would be a better choice especially since it has crossfire support. The only this with the motherboard you picked is, I've heard that MSI removed support for 125W CPUs from the k9a2 cf because some people were having issues. I think that's kinda crappy to remove support for CPUs, but oh well. For the phenom I would recommend this board
ASRock A780GXE $79.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157139
Because the 780G chipset does not normally support splitting the 16x PCI-E lanes evenly between two slots ASRock took a page from their Radeion X1600 days where they used a small circuit board to switch between 1 16x slot and 2 8x slots. Actually that board looks almost exactly the same to me as their X1600 boards that I built a few systems on. A better board would be
ASRock A790GXH $94.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157156
or
GIGABYTE GA-MA790X-UD4P $109.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128387
Since 790GX boards have the SB750 which has ACC to help better overclock your phenom CPU. If you know what you're doing the ASRock board is a good choice since it has many overclocking options, but they usually aren't newb friendly. If you're new to overclocking you will appreciate the easier to use Gigabyte board. Also make sure to get an aftermarket cooler for the 7750 because the stock cooler it comes with may be great for 65W Athlon X2s, but it doesn't do too well with the heat of an overclocked Phenom.