dieselpowered, the United States Government issued a warning against the use of Internet Explorer browsers, in gov buildings I've noticed they don't tend to use IE anymore.
I used to make my sites not work for IE versions, but regardless always suggest Firefox or Opera (Firefox is pretty crappy these days but for most people it's golden, it eats over a gig of ram for me though :( )
IE8 takes like 30 seconds just to open for me, I only use it for windows updates.
Try the firefox beta, renders IPB3 JS even quicker then normal firefox...
but no it's the actual execution of IPB3 that is slow, on every test instance since the first ioncube beta I tried it has executed SLOWLY and I don't get why... I enjoyed having IPB2 boards load in less then 1 second.