John Resig has a performance rundown that is about one year old that included IE (http://ejohn.org/blog/javascript-performance-rundown/). IE is woefully slow compared to the other browsers in the roundup and is not included in some of the results as it would continually crash during testing. It would be nice to see some more up to date benchmarking with IE, but the link I referenced can give you some insight as to its speed relative to the other browsers.