Sad to say decided this week that the ppd on the opteron isn't worth the cost compared to the GPU's. I was getting about 300 ppd/watt on the opteron, but about 1150 ppd/watt on the two 970's. Not sure if I'll sell or not yet.
i have had to drop too i have just 2 970s folding as the 2 780s will be used when i game now but not very often