The 64-Bit Story
Our tests of Vista's 64-bit version indicate that while programs generally run slower on it than they do on the 32-bit version, adding more RAM can help wipe out the difference (see the "Apps Run Faster on 32-Bit Vista" test report). With 1GB installed RAM, the Polywell and Micro Express PCs ran our Photoshop test 12 percent and 25 percent slower, respectively, in 64-bit Vista. When we moved both systems up to 2GB, the difference disappeared completely.
The delta on the multitasking test was much smaller--between 4 and 7 percent, regardless of the PC's memory configuration--and our gaming test results showed almost no difference. We don't know how often hardware vendors will put their latest drivers through the full testing and signing process for 64-bit Vista, but these initial results suggest that, as long as your system packs plenty of memory, you won't be taking much of a hit by going 64-bit.