64-bit performance increase is expected to be huge, but I dont know.
Only in apps that can really benifit from it, like compling, some games, stuff like that. Most common users (not the most common NBF users, I mean to 90% of PC users in the rest of the world that just do office, internet & email type stuff ) won't notice the difference.
the projected 64-bit performance increase is 15-20% over the equal 32bit counterpart. i've been using a 64 bit OS for over a year now and that seems to be the case. but luckily for me 95% of my software is compiled for 64-bit