RightJS, on the start was real fast on the WebKit browsers and just above average on other browsers. The difference is that on WebKit browsers it was using the native css-selectors. But after an optimization session on the RightJS manual css-selectors, now we can proudly say, that RightJS kicks all the other frameworks on almost any browser and any conditions.
Check it out on the page RightJS Benchmarks, there are tests for all the modern browsers, including IE and Opera. There's no test results for IE6 yet, because it has some memory leaking issues which were not fixed yet and slows the browser down. But rest of the results looks cool