Hey guys, I recently flashed my 6950 to the 6970 and it appears to work perfectly. Last night while I was playing rift on ultra settings I decided to oc the card in the ccc using overdrive. I pushed it immediately to 950 / 1450. It would work for about 5 mins then freeze for about a minute. It did this continuously until I returned the default settings in ccc.
Pushing the card up to those speeds can cause instability for a number of reasons. The power supply unit is being overworked, too much heat generated in the card, the card itself needs more core voltage, mem voltage, and what I think is the problem, you are overclocking the card too high. 950 is pretty high on air and 1450 is pretty ridiculous. Try 925/1250
Agreed. Those settings are pretty aggressive, especially for an air cooled, unlocked card. The freezing is certainly caused by instability. To give you an idea of how insane your 1450MHz memory frequency is keep in mind that GDDR5 runs at 4 times the clock speed to set it at, so multiply 1450MHz by 4 you get an effective transfer rate of 5800M Transfers/Second.
To get your card stable you'll either have to jack up your voltages (not recommended because of the heat and stress on the GPU), or lower your speed down to something more reasonable. Like marlon said, 925/1250 are more reasonable speeds.
GPUs are not like CPUs when it comes to overclocking, GPUs have far less headroom to overclock. GPUs are not a like a Phenom that you can overclock 30% or a i7 that can go from 2.8GHz to 4GHz. GPUs have more aggressive factory clock speeds than recent CPUs do in order to get the best benchmarks possible with a factory configuration.