Ignoring the gpu usage reported, what hashrates are you getting? Max you should get about .6MH per Mhz of engine clock speed.
Well, it's hard to ignore the reported GPU usage, since I've been noticing that low GPU usage corresponds to low hashrate, and high GPU usage corresponds to high hashrate. So while the cards might be capable of hitting 550MH/s at stock settings, when I run all the GPU's in tandem I might only be hitting 450-480MH/s per GPU. I'm noticing about .5MH/s per MHz.Also, I just used ATIman to do a clean uninstall and re-install of 11.12 and the 2.6 SDK, and cgminer is crashing when I choose a single GPU or all GPU's for mining. Do I need to compile for Windows from the latest commit?
And by the way, ckolivas, do you have any recommendations for Linux (Ubuntu) drivers + SDK for a rig with 7x 7970's? I've been reading around that some people like 12.2 + 2.6 for 2x 7970's, but is it different somehow with 7x 7970's? I forget if AMD's Linux drivers have a GPU limitation like they do in Windows.
How does one edit the BIOS of 7970? RBE doesn't support it 
The old fashioned way, with a hex editor. RBE should be able to support 7970 bios editing, but the dev seems to believe that there are new security mechanisms to prevent BIOS editing.. which there aren't.This post over on the OCN forums outlines how to edit the 7970 bios to change clocks and voltages:
http://www.overclock.net/t/1196856/official-amd-radeon-hd-7950-7970-owners-thread/4220#post_16496161