Coolbit values are stored in registry in keys that are named after the Simpson family (Bart, marge, home etc)
Do a search in regedit for any of these.
Then set the value for GPU speed to the lowest avail in coolbits and then refresh the regedit window.
You will see that a value has changed and that value is also now the same as another value remember that other value (the key name) and then set the GPU speed to the value where you know your GPU is completly stable, prefrebly not to close to the edge.
Refresh regedit again, now that value has changed again as it did before, take that value and put it in the other value I told you to remember so that they are the same.
That's how you get beyond the Coolbit limitations.
I used this before but I don't have a videocard at the moment so I can't confirm that this method still works but I assume it does.
I know rivatuner is a lot better and easier but it's allways good to know that there is a way around it.