The PeaceKeeper benchmark isn't really an accurate description of javascript performance - they're using js timers to do the timing for starters, which given the accuracy of a js timer in milliseconds (anyone who's ever tried to use one and have it be anywhere near accurate knows the horrors I speak of) means you could have a browser score 9,000 when it's nowhere close to that score, or the converse - a browser that doesn't update date.now quickly will have a poor score. Also, the fact that the test turns some of the operations into no-ops as the test runs (but still counts the no-op times.... wtf???) means a browser that can handle a no-op that you will never see in real life the fastest, or that updates (specifically) Date.Now() will have a higher score than ones that do not. Neither of these are real-world areas of pain, but they play a very large part in the PeaceKeeper score. Top it off with running inside a Java VM (and the browser's ability to run Java code faster will have an impact on the ultimate score) means it's a crap benchmark, because it has nothing to do with the real world nor is it laid out with actual performance testing in mind - it just tests some "things" and the fastest browser at those "things" that are in no way real-world tests will get a huge score.
The test, frankly, is a disaster and not very accurate. Heck, sunspider is more accurate at least at timing the execution of certain js functions, and we already know that test is wildly inaccurate because some browser makers have been tweaking their js engine load-times so that these tests look faster too. It is what it is, and using a multitude of benchmarks are nice, but what is really a good idea is to clear your cache and visit the sites you normally visit and see which browser is fastest at doing what *you* do with a browser, not testing random js functions or HTML4 or 5, or some CSS or DOM functions, and determining which is faster at a "test". The best test is which one works the way you work, and runs the sites you use without getting in your way.
Really, that is the best benchmark.