This site does a great job of doing a browser speed comparisons. It is not just a Windows only, it includes Linux and Macintosh. It is also not just a comparison of the most popular browsers, such as Internet Explorer, and Firefox. The comparison includes, browsers that I have never heard of before. The results are suprising and detailed.
Below is an excerpt from the site: "There is a speed war on the web. Browsers compete on many fronts; security, standards support, features and speed. Most people are aware of which major browser fails on three of these, but one of them is still open for grabs. Speed."