Better - and, consequently, more expensive - hardware is only able to realize its full potential when overclocked. At default speeds, many memory chips run far below their maximum specification.
In this o/c test, all cards were pushed to their respective limits. These results should be taken with a grain of salt or two, since companies have been known to send out especially potent overclockers to reviewers to skew the results in their favor. Besides, even within a product family, a certain spread is always possible.
These results should therefore be seen as a rough indication of a card's potential, and are in no way a guarantee that your model will reach the same speeds! The tests were run in Quake 3, at 1024x768-32:
The number in parentheses behind the product name denotes the maximum attainable clock speed. Measurements were taken with an open case and without additional cooling, at a constant ambient temperature of 22°C.