A processor's clock speed is derived from the system base clock, which is 266 MHz in the case of the Intel FSB 1066 bus, multiplied by a so-called clock multiplier. The Core 2 Duo E6300 runs at 1,866 MHz (1.86 GHz), which it reaches by multiplying 266 MHz by 7.
It would be just perfect to select a higher core clock speed by increasing the multiplier, but unfortunately the CPU manufacturers lock the multiplier at the default value.
This means that the only way to run a processor beyond its rated clock speed is to increase the system clock speed.
Current platforms such as the P965 chipset offer great overclocking margins, but be sure that you know of the dependencies related to the system clock: the main memory clock speed is derived from the base clock as well. If you increase the 266 MHz base clock to 333 MHz, the memory will be running at the same 25% clock speed increase.
In turn, this means that you either have to purchase high-performance memory for overclocking, or you have to set the memory to a slower speed, so it still works at your preferred overclocking settings.
How to Calculate CPU Speed
There are a lot of utilities to show CPU and FSB info. Two of the most popular are:
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In particular PC Wizard can show not only CPU/FSB info, but also a lot of other RAM and general system info / hardware configuration.