With the little information you've supplied, our miracle department is off on the weekends!
There are so many factors as to why some can reach certain clocks and some not.
1. The quality level and stepping of the CPU!
2. The overclock ability of the rest of the hardware!
3. BIOS settings off somewhere!
4. Lack of overclocking knowledge!
5. Poor case airflow and CPU cooling solution!
6. Lack of component specification knowledge!
7. Not enough Vcore applied!
8. Running the system memory past it's capabilities!
9. Not enough NB voltage!
Etc. etc. Unless we can sit down at your computer, see what you have done to fully understand what is keeping it from going further or if it even can go further, all you'll get is suggestions and guesstimates as to the solution!
You may actually be at your CPU's max clock now and don't realize it, simply because even though you may have seen others get better results, you have no idea of their overclocking knowledge, or cooling they're using to get there.
You also have no idea if their overclocks are a one time fluke that barely stayed stable long enough to make a CPU-Z validation or completely 24/7 100% stable, so you don't know the full validity of what you've even read, you've trusted it to be true.
And you're not providing enough information for anyone here to seriously help you, except maybe Criss Angel!