I just got this board today, upgraded from a Gigabyte H81.amp-UP that I somehow killed. Same cards (R9 270x), same OS install (usb stick, BAMT 1.6.x) and I was getting about a 50+ Kh/s increase per card!
Only thing I changed was the board, cpu/ram (old ones not compatible with new board) and a different power supply. I'm going to play with the settings a bit and see if I can get the cards to stably hash at 500Kh/s. My last setup was getting 440Kh/s with a ton of tuning, so I was rather shocked.
I'm shocked too. My Gigabyte R9 270 is hashing at 480kh/s right now...