I have the same cards on a rig with 13.12 : 470H/s per card (280X)
but 280H/s with 14.6, with or without the opencl files in the directory.
VTX card, Hynix memory.
I have 3 rigs with 14.6, with the 13.2 opencl files in miner directory, 470H/s per 280x,2260H/s with 6X 270
When without the opencl files speed going low .