The 64-bit version's really only required for longer or very heavy sessions, for more general usage of a 3-8 hours or so, the x86 will likely prove fine and not require as many resources, so better for lower powered PCs as well.
I was not looking at this as what is required or better. No doubt 64-bit Windows will support a 32-bit browser so that is not the issue. But I will say, the "hours" one uses a browser (or any program, including the OS) has no bearing at all on whether 32-bit or 64-bit is better.
And the reality is, with the exception of the OS itself, the difference in the amount of resources the 64-bit program uses vs the 32-bit version (assuming the same features and configuration in each) is negligible. As a test, I have both the 32-bit and the 64-bit version of PM on my test system. I fired up the 32-bit with the home page set to
Google and Task Manger said I was using 132MB of RAM. I then exited that and started the 64-bit version to the same home page and Task Manager reported using 144MB. If a system is taken down because of that extra 12MB, there are other issues and that is an exception, not the norm.
So while it would not make sense to use, and you are not likely to see a 64-bit OS on a system with only 2GB of RAM, there really is no reason you cannot use a 64-bit program if there was a 64-bit OS installed.
That said, the reality today is most computers are running 64-bit Windows and have more than 2GB of RAM installed. So the point I was trying to make by starting this thread is if you were using the 32-bit version because
years ago, 64-bit add-on support was limited or because the 64-bit version of PM was buggy, those appear to no longer be issues.