As for the other browsers in Apple's claim: compared to Chrome 5.0, Safari 5 was 3.5 percent faster in our test. Safari 5 was well over twice as fast as FireFox 3.6. Our results actually find Safari 5 faster than what Apple claimed--again, Internet connectivity can influence test results.
Apple didn't mention Opera in its speed claims, but we tested Opera 10.53. We found that Safari 5 was 11.5 percent faster.
One thing to keep in mind is that the differences are measured in milliseconds, so you may not be able to sense a difference between Safari 4 and Safari 5.