These results are from Apple's own team.
HTML Benchmark (win/mac in seconds)
Safari 4 - 1.01 / 1.15
Firefox 3 - 3.21 / 3.81
Javascript Benchmark
Safari 4 - 0.18 / 0.14
Firefox 3 - 0.82 / 1.73
Safari is slightly quicker with JS on Mac, but HTML is faster on Windows. And FF is faster with windows in all aspects. Interesting to see Safari render quicker on Windows. Though I guess it depends on how much JS is being used on a page which would ultimately load quickest.
There's a link to a performance chart near the bottom of the page which includes other browsers.
http://www.apple.com/macosx/refinements/
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