I haven't got a clue why this hasn't worked for you ? I won't be adding 11.6 to linuxcoin anyway it's very VERY unstable, stick with 11.5 for now.
I got it working now and 11.6 does allow you to overclock outside of BIOS limits. The problem is that I was not installing the drivers properly. The driver seems stable in Ubuntu 11.06, but I guess it has different versions of X and other software.