Only thing that I see that the miner stops mining for 500~900ms every so often for me. The hashrate reported in the miner doesn't seem to be the same on the pools. Maybe a possibility that the miner has a glitch to stop mining for ms of time and/or the share ain't being sent correctly for Windows. I have 3x HD 7970 that do ~68 MHS. When I enter that hashrate, it reports that I should get approximately 4.70 Ether. Instead, I'm averaging around 3 Ether a day.
Ok but at least you are mining some ether. What was the guide that you followed to get your miners working?