Win7 is still shiny-new, perhaps we need to give some time for driver writers etc to get up to speed. After all, XP video drivers are still tuned today, after so many years, sometimes with significant performance gains in specific cases. If you have a WDDM 1.1 driver - new for Windows 7 - chances are that it will be tuned and will become a lot quicker in the coming months, the goal for the initial release certainly being stability over performance. There is nothing in FPV that would slow down in 64-bit mode, and the much greater available memory should make things faster and smoother.
If you don't
use the GPU-accelerated mode, we made a change in a recent version that is actually slowing down the program a little in exchange for better image quality: the filtering algorithm used is now better if you check the "High quality downscaling" option, and the previous "high quality" - which was bi-linear filtering - is the new "low quality" (when the option is unchecked). You may want to uncheck this option to get to the old quality/speed compromise.
This option has no effect on speed when the GPU mode it turned on, and its effectiveness is entirely governed by the graphic card's abilities, in particular the card must support multisampling to get smooth pixels in fit-to-window mode.
TIP: Be sure to exclude the image folders from being scanned by your AV. You can also put FastPictureViewer.exe on the exclusion list of your AV scanner, in order to prevent the anti-virus to scan all images opened by the program. Kasperky 2010 users also have to option to exclude digitally signed programs (that would include FastPictureViewer and all the codecs it uses) : http://support.kaspersky.com/faq/?qid=208280683