Since many years I am married with the opera web-browser. Besides a hundred reasons (intelligent features, versatility, configurability to excess, lightweightedness, dozens of practical things, ease of use etc) it was exactly the speed issue that impressed me most. you just can literally feel the smoothness and speed how opera is able to handle 15 open tabs (web-adresses) compared to for example with the so much acclaimed firefox. there was no need to have it proven by some benchmark, the difference can be experienced by just using it.
but yesterday I stumbled over a website of some diehard firefox-user. as a web-programmer he decided to write a bench(mark) on javascript interpretation-speed. and then tested some browser on it.
well,
, .... he is still busy to rearrange his dropped jaws.you can jump to his website right here and do some testing on your own.
for everybody's convenience here are my test-results:
edit: tested on GA-5AX rev 5.2, K6-3@550, 768MB ram, NT4 Svp6a
L 
) that Opera functions way faster than the rest of the other browsers of the day. To do his day, I still have this feeling when I am running Opera (as to other times I use IE to get updates from microsoft, it seems to take much longer. I suppose any Opera user does not need this test to prove how their browser is.