Dont mine and play games at the same time that's the problem
This is probably the easiest and best solution.
I too have a 7970 that I game and mine with but I never do both at once. You might try setting a low intensity as opposed to using dynamic intensity. Dynamic intensity never gave me good results, even when I wasn't using the system for anything but mining. Anyway, even though I shut down cgminer before I fire up games, I've still gotten the issue that you describe. The solution that I've found is to increase voltage (assuming your card is undervolted) or decrease clock speeds. My 7970s mine away happily at 1000mhz and 1010mV. I've literally mined for weeks straight without a single hardware error only to open up Guild Wars and be inundated with graphical artifacts and driver crashes. What I found was bumping up the voltage solved the problem (1010mV -> 1030mV). Apparently games need a little more voltage than mining which is kind of counterintuitive and weird seeing as how mining is so intensive.
In your case, you mentioned clocking the card down which should certainly help if your problem was similar to mine. It may be that your issue is different.
I hope you can get things resolved. Good luck