I really don't think it's very important that it is though. Whether their JS engine two (ten?) times slower than another won't really matter for the majority of

I really don't think it's very important that it is though. Whether their JS engine two (ten?) times slower than another won't really matter for the majority of browsing. They've really improved the rendering engine and standards support but the experience of the application as a whole is still way behind their competition. Modern IEs failings come from a collection of bad/sloppy UX choices.