So I have a few Radeon cards laying around and I thought I would see what they can push as far as mining. Unfortunately my main gaming rig is all Nvidia powered and I didn't realize the huge difference between the two companies as far as sha256 hashing.
Anyhow with that said I tried out xubuntu from a guide I found on the net, its a bit more complex to set up but was able to get it running but for some reason I was only seeing around 250, and well while the overclock tools or the various drivers I had to track down and try didnt seem to help. I booted up the same box with a vanilla windows 7 with sp1, installed the proper recommended ati sdk 2.1 and c 11.12 drivers. I also downloaded amd clocking tool and bumped up my core to 980 with memory at 300, no voltage change and boom I was mining at around 450 average for the same card.
Here is an included screenshot of the details.