I just ran DOMAssistant's latest slickspeed benchmark and I must say that DOMAssistant looks sharp.
Of particular interest is the ".note" test. I just wish they added benchmarks on more practical queries like ".class tag" or ".class .class". They do have "tag.class tag.class", but since the optimum algorithms for these queries is somewhat different (especially in less capable browsers), I think those cases are all relevant.
Another thing that is worth pointing out is that library authors could put a bit more effort in testing in IE6. There are way too many tests with inconsistent number of elements returned. It's true that "p:nth-child(even)" isn't a very realistic test, but "div + p" and "div:not(.example)" are not that far fetched.
Anyways, did anyone notice that the legend at the bottom is broken in IE6? :)