A Second Shot: Windows Vista SP1
 

Compared to where we were a year ago, our general recommendation for Vista is unchanged. We are however impressed with the progress of the x64 versions of Vista over the past year, after feeling like it was lagging behind Vista x86 from beta up through the release version of Vista. Vista x64 is now clearly on par with Vista x86 and we have no concerns about its compatibility or performance. There are still good reasons to stick with Vista x86, such as compatibility with specific applications and Vista x64’s higher memory usage due to WoW64, but these are the only reasons. A year ago we recommended using Vista x86 unless you specifically needed Vista x64; now we’re comfortable making the opposite recommendation of running Vista x64 unless you have a specific reason to stick with Vista x86.

http://www.anandtech.com/systems/sho...spx?i=3233&p=1