problem overclocking video card

[TurnX]

I have an ATI X1800XT 512mb Crossfire Edition video card. I was doing some overclocking on it last night and im having a big problem with it. I was fowllowing a guide online that I found, mainly for pointeres, using ATI Tool to monitor temps and voltage and overclcoker to set the core/mem frequencies. All seemed to be working well, I got the clock from 600 to 650 and the mem from 700 to 800 and the temp was holding steady at 33C at idel with the fan at 50%. I then ran 3dmark 06 to test the card to make sure it was stable and to see how well the overclock helped. However when it copleted I had a score of 3865, but when I ran it without and overclock I got a 3985. Any ideas on what could be casuing this because as far as I know an overclock should increase your scores.