His miner is probably displaying the wrong numbers, no idea why tho. I'm willing to bet whatever pool he mines on reports closer to 600kh/s per card. With major overoclocking djm said he was able to get 660-670kh/s
Yes. As stated in my previous post, my miner (SP fork fork of ccminer -
http://github.com/sp-hash/ccminer) is displaying higher hash rate than what's reported by the pool. I'm getting 620-625 kh/s per the pool. On my EVGAs the gain from overclocking is quite small.