Is the speed improvement any better with the 64 bit edition of XP, or do we have to wait for the "64 bit version" of windows media encoder to even test it? (XP 64 bit edition is a free beta right now, you can download a 365 day license).
Actually windows x64 is being designed with the mindset of a need for improved performance with digital content creation, floating point, and anything that addresses large amounts of memory. So yes, you will see performance gains. I don't think they will be shocking though, or atleast not yet anyways.
I'm also not going to rush out to buy 64bit versions of the software that I own today. More than likely it will simply phase itself (64 bit computing) in gradually, say about ten years from now?
64 bit programs will just get faster and better as we learn to write cleaner and better code. Plus, with 64 bits to address instead of 32, you will see a great performance gain. I am not saying 64 will stick around forever, eventually it (may) be phased out to 128 bit or 256 bit computing or something else entirely. I can't really give you a timeframe when though.