It is strongly suggested for most people to disable any kind of setting that causes dynamic performance changes when they are OCing.
C1E and stuff like that as well as turbo core and stuff like that should ideally all be shut off when OCing.
If you have a stable system with those things turned off, you can slow roll turning them on and see if they case stability issues. Most people just leave them off, though, I think.
Also, what are you doing when the freezes/crashes occur?
The first thing when I think freeze during gaming (if that is what is happening) is that a bad case is putting serious strain on a PSU to the point where it can't adequately power the video card anymore.