When you talk about browser benchmarks a lot of people refer to sites like Sunspider, but these only test raw performance with micro benchmarks, which can show major differences between browser speeds BUT they are very bad at showing real life browser usage.
A friend recently showed me a better set of benchmarks, called Peacekeeper. These tests try to emulate real world usage, and they show a very different picture.
Peacekeeper Scores (Higher is better, All run on Windows 7 RC on the same machine)
IE8 = 422
Firefox 3.0.10 = 688
Chrome 2.0 = 1207
Safari 4.0 = 1423
This shows that Safari 4 is only 3.5 times faster than IE8. This is dramatically different, from Sunspider which shows Safari 4 to be 37x faster. The difference between Firefox 3.0 and IE8 is even less. Firefox 3.0 is only 50% faster than IE8.
Now all of this still probably only milliseconds worth of differences between browsers and a browser is much more than its performance, for example i think IE8’s RSS manager is a lot better than Safari 4’s, then there’s the UI to consider, and most importantly how long it takes to start the browser.