Don't MSI 7950's and Sapphires exhaust out the back (through the bracket vents)? If so, aren't the box fans on the wrong side of the the rigs? Essentially it looks like you're blowing back into the exhausts.
Unless those box fans are facing the other way and you're actually pulling the hot air away... hard to tell.
None of those cards dump heat out the back, they just toss it out whichever way they feel like. Look at the cooler design on any 280x (or 7950TF3) you'll see what I mean.
Only the ref cards really exhaust out the back.