IE64 is faster than chrome in the same way waterfox is faster than firefox, however oddly, you cannot set ie64 as the default browser.
It's interesting in two ways. Firstly Ms made huge effort with IE8/9, they pushed it in the same way they pushed directx 10 with windows 7, and made a similarly large effort to comply with standard they'd previously ignored (the lifehacker article above is good, concise summary). They succedded with directx, despite opengl being a more powerful,better option but failed with IE through a combination of stigma and lack of flash support.
Now all the important plugins support x64, but IEx64 which was the fastest html5 browser when it launched is scoring 1/4 of what firefox scores in the peacekeeper html5 bench. It seems MS are still stuck in the trap of releasing a browser then doing nothing for 2 years until the next one is released.
If you have to use IE then the x64 build is a no-brainer imo, but the inability to set it as default and having to pin it tot he task-bar is a pain too imo. If you ever click on anything that opens the browser it'll be the x86 one you get.