well i used XP64 for around a year and a half and i loved it. i have now been using vista x64 ultimate (cheers for having friends at MS) for 2 months and its one great OS. everything runs just fine and as long as you have a pretty good system im sure it will be the same for you.
one thing is vista boots faster for me then xp did even with my 5 harddrives and 2 dvd drives