I use Flare 7 on a core i7 64bit windows machine with 8GB of ram. It is definitely using multiple cores and more than 3gig of Ram during builds. The xml editor is no more faster or less buggy on 64bit windows, so day-to-day writing is about the same.
Here are some rough build times using my two machines on a 2000 page PDF build:
32bit Win 7, 2.4Ghz Intel Core 2 Duo w/2GB Ram : 1 hour 10 minutes.
64bit Win 7, 2.0Ghz 2nd Generation Core i7 w/8GB Ram: 35 minutes.
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