You won't notice a difference between a 1045t and a 1055t.
I don't know that the stock clock speed will be "bad" with a powerful graphics card. Mine was just already overclocked when I went SLI.
IIRC, it did fine with the single GTX 560 at stock clock, but that's less GPU than the single card you are looking at.
If you want a decent AMD chip for gaming, check out the 965 or one of the other quad-cores with clocks higher than the 1045t.
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103727