I only get 12300, and my gpu is reasonably overclocked and my cpu is at 3ghz.

Your score of 11800 is about correct, as your gpu is only very slightly overclocked and and your cpu is at stock. If you bumped your cpu to about 3.5ghz then you would get about 13500.

3d mark 06 places a lot of importance on the cpu, so I would not take it too seriously. As long as you are running the games fine, then I would not worry.