Forgot to mention, I kept seeing the MHash drop off when the screen would disable even though I configured Ubuntu to ignore all power saving settings; whenever I'd wake the screen up by jiggling the mouse or hitting a keystroke, it would be sub-300 but then on the next workunit jump right back up to 312+.
My solution, since this is a dedicated mining rig, was to set the session to xterm, and use AMDOverdrvCtrl with the -b flag to load a saved .ovdr profile followed by calling out Phoenix. In this way I was able to eliminate the performance drop, and also since I have the system on UPS and set to auto-reboot / auto-logon, I basically have a bulletproof bitcoin dispenser
My solution, since this is a dedicated mining rig, was to set the session to xterm, and use AMDOverdrvCtrl with the -b flag to load a saved .ovdr profile followed by calling out Phoenix. In this way I was able to eliminate the performance drop, and also since I have the system on UPS and set to auto-reboot / auto-logon, I basically have a bulletproof bitcoin dispenser