I've update to the Beta drivers 340.88 and the hash increased slightly. Now getting 7.1 Mh or so but still not the 7.8/7.9 Mh you are getting. I also tried with minep.it pool but as I was expecting it didn't change anything.
Any more ideas?
I have not followed the whole conversation, but I am wondering if one of you is running on risers and the other not?
That's an interesting theory. I read somewhere that indeed it could affect the hash rate
http://cryptomining-blog.com/1276-first-impressions-from-a-6-card-mining-rig-using-geforce-gtx-750-ti-gpus/I, on my side am using risers. Powered for that matter. The difference it rather significant: ~800/900 Kh
I am also using ASUS, not Gigabyte. Perhaps that could also be the reason.