Think of CPU power as horsepower though. Its not always going to run at its max speed, if it did then it would probably blow up in short time. Your car might say it has 300 horsepower but that's only when the RPMS is running at 5000 RPMS or so in which your not always running your car constantly at 5k RPMS, errr.. I hope not
Where are you seeing that your CPU is lower though, tells us exactly what the problem might be. If its your system stating its that speed of a processor, take the advice above. If you have some tool that is showing you real time cpu speed, read the first part of my post here.