You COULD drop down to a 7870 and Overclock it. They overclock very well and can perform better than a stock 7950, for ~$60 less.
Other than that I like your build.
Nah, I wouldn't sacrifice that 3GB of 384-bit memory. Plus you can overclock the 7950 to surpass the HD 7970, so the question comes back to budget. Also, Techreport.com shows a significantly smoother experience on the 7950 over the 7870.