Why not try 7950s? Although they have slightly lower Hashrates they're still quite cheaper than the 7970s.
Yes 7950s are a viable choice. Here in europe I compared the price and you getting excactly the same hashrate for your buck than with the 7970s.
I would definately open the case up, or put one of your case fans (if you have spare, like the ones on the top, or at hdd bay) to blow air right on to the cards.