I'm getting about 320Mhps per card out of my HD6950's but my temp is hellacious at 85C+! I double sided sticky-taped an 80mm fan to the butt end
of both HD6950's and it seemed to help keep it at 80C but only if the side is open. I'm hoping to add a few more fans in a day or so... these things crank out the heat!!!!
A side fan blowing air OUT of the case might help. If your case does not have a place to mount a side fan, you could cut a hole in the side panel or buy a replacement side panel that already has a fan mount. I think I'm getting about a 1.5C drop on my hotter card when I installed a 120mm fan in the side. I think that might help you.
I like how you have your 120mm fan attached to the end of the cards, but if anyone has a solution that is more resistant to prolonged exposure to high heat, please post. I'd be worried that the sticky stuff in those little white squares would get slippery or brittle over time. I remember when PCs had rubber bands bundling wires ... until they got brittle, broke, and caused all sorts of problems.