<blockquote>Question: Intel's Sandy Bridge launch just brought its desktop CPU line up to 3.8GHz, but I remember that the Pentium 4 got up to 3.8GHz before being cancelled. So why is it that Sandy Bridge is just now getting to the clock speed levels that the Pentium 4 was at years ago? And how is it that Sandy Bridge still manages to outperform the older Pentium 4, even though it has a lower clock speed?</blockquote>
via <a href="http://arstechnica.com/ask-ars/2011/04/ask-ars-whats-the-relationship-between-cpu-clockspeed-and-performance.ars">Ask Ars: what's the relationship between CPU clockspeed and performance?</a>.

Worth a read.