What you are seeing is a feature in all of Intels CPUs called Speedstep. It will lower the clock speed of the CPU when it is not in use or under heavy load. Normally it will stay at the 2GHz range when its at about 20% load and bump up to 2.5GHz above 20% load.
To do this it adjusts the multiplier to a lower setting. Yours is 7.5 as a max and low of 6.
If you load a program that uses the CPU heavily and run CPUz, it will bump up to 2.5GHz.
Just as a example:
I have a Q6600 overclocked to 3GHz. When its under load, it runs at 3GHz which is 9x333MHz. When its not under load it runs at 2GHz which is 6x333MHz.
For your CPU it would be the same so:
Low
6x333MHz = 2GHz
High
7.5x333MHz = 2.5GHz
It wont affect your performance because when you need the speed, it jumps up to it.