When I still had my 8-gpu rig consisting of MSI Gaming X 580 4gb elpidas, I'm having similar problems as you. They're smooth and all but they only hash 29.6 if all eight cards are connected.
If I only plug 4-5 cards, they hash a terrific 30.1 up to 30.3 each.
I've created a thread here, in another board and even in ethermining sub of reddit but apparently, not too many miners have 8-gpu rigs to contribute their thoughts.
I'm in the process of building 8x Nitro+ 580s on Saturday and I hope and pray that it's not going to be the same experience as the Gaming X's.
lol... I've got seven 570 rigs with 8*MSI gaming, 8*asus expedition, and 8*Nitro+
mostly elpida, some of those also have 2-4*1060 Palits 6Gb all on Asrock h100 btc.
The issues I'm having with dual claymore v10 & blockchain drivers:
1) the main problem is that some cards like to go down to 24-25 from regular 28-29. On some rigs first boot is almost guaranteed to be this way, often it's 28,25,25,25,25,25,25,25... but on anothers it may come in a few hours after reboot. (if it comes later the cards become very unstable and often crash, even on 1800Mem and 1080Core settings. Didn't check the stock timings yet...) Sometimes these all can lead to win hung, but now just installed watchdogs, so this is partially solved:)
2) Another issue is that Nvidia may fail to allocate dag and several reboots(sometimes even 5-6) may be required to get rid of this error. Also may lead to win hang.
3) And finally extremely irritating issue with EthMon: I've got one rig (one of the clones, so nothing special about it) that after 10-20 hours looses connection to EthMon, and will appear red, although working fine.
