I was curious to know before I order my second pair of cards if I could successfully run 2 Gigabyte WF3 and 2 ASUS DCII (R9 280X) GPUs on the same rig. I assume that I should have no issue because they are nearly identical aside from power delivery and cooler design.. But hey, stranger things have happened.
from Litecoin mining! http://www.reddit.com/r/litecoinmining/comments/1tslqa/using_more_than_one_brand_gpu_on_a_mobo/