performance wise though i reckon you are best off doing a clean install. it will pay off in the end and it will only take an extra hour or so re-install drivers and such. especially if you are migrating from a 32 bit os.
download all the installers for the things you want and place them with with all files you want backed up (pictures, savegames, videos, bookmarks, etc ) together on a seperate hardrive. that way, on your OS installation hardrive, win7 can be installed all fresh and clean and then as soon as it is installed you can start instaling the programs and stuff you want straight away rather than waiting for things to download.
as for drivers, win7 is pretty damn good at auto installing them on first boot.
also, have a look at this which saves quite a bit of time http://ninite.com/