32 vs 64 has not much to do with W7 EOS
It has to do with Hardware installed in your PC. (and 64 would not install if you did not have a 64 bit CPU)
You can have both installed (and this might be a good thing if you use some of the older PI that have not been upgraded in a while) You just run ONLY 1 version of Calibre at a time and use the PI as needed. So havin 32 bit be a 3.x version and 4.4 be your 64 bit would make sense
At this time, the DB is the same.
Kovid will warn us if it ever changes to the point old Calibre will have issues
