Some say you get better performance mining in linux versus windows.  I can't vouch for that claim myself.  The biggest problem I've had for mining in linux (beyond learning how to use linux itself) is overclocking in linux.  AMDoverclockctrl seems to be the way to go as far as overclocking in linux goes.  However, 6950s are limited to 840mhz for the core through the bios.  As far as I know, there is no way around this for software in linux.  Windows has several programs that will allow you to bypass the bios limit.
It looks as though a bios modification program called RBE for windows has some options that I am looking into myself.  It looks like there might be possibility, but I am not sure if it's really worth the hassle and risk of reflashing with a bios I modified myself.
If any of you look into RBE bios modification in terms of the increasing the overdrive limit and such, be sure to open RBE and read the warning concerning 'method 2 - no hash'.

There is a 'clock settings' tab on RBE, but I am not sure if you can go over the limit with just that alone.  It looks promising, but there is risk involved and I have too much uncertainty concerning the idea.