Windows 7 x64(64 bit) could use up to 192GB ram
Is more better? Well, depends on the software you use. Does it use more, and do you run multiple programs and does the software use a lot of ram. If you run like couple of software that use like 512MB of ram at a time. I dont think you need 32GB. But if you run soft ware that use 4GB here, another software 4GB there. I think Windows OS use around 2GB. Right now for me it is using 2.3GB out of 16GB. I also turn off pagefile. If you are going to play 1 game at a time, or watch movies, or just surf the web. I think 16GB is more than enough.
You could always get the ram first and see does it work. If it doesn't then put back the ram that did work in the pc, and flash upgrade it then.