You will need SGMiner 4.0.0.
CGMiner doesn't like mixing different -g 1 and -g 2 (gpu thread) cards in the same config.
That's what I was looking for. Thanks. I'll be running two 7950 and two R9280x on one system with xubuntu 12.04. Can't I run two instances of cgminer one handling 7950s and one with R9's?