That limit was put in a long long time ago. 12.5 or 12.6 I think. You should not have still been on 12.1 and you should definitely not go back as their drivers are much, much improved with huge performance gains. You should absolutely update CCC too and there is no reason to remove it. You need it if you expect things to work right.
Uninstall gpu tweak and install a newer version that still allows the overclocking range enhancement. enabling it should undo the lock. I think my version is 2.25 but I am fuzzy on that. They took it out at one point, i think because of windows 8, and I'm not sure if they put it back on the newest version or not.
In any case you'd get more out of the driver than you did out of your overclock so the correct thing to do is ALWAYS keep your drivers up to date and google how to undo the overclock lock.