cpu architecture doesnt have anything to do with security, its jsut how many bits per clock tick it can push in and out of the CPU. When it comes to security the more bits in your key the better but has nothing to do with the CPU as RSA keys can be up to 2,048 bits.
64 bit has standard for over 10 years now, people who were installing 32bit since with windows Vista were doing it by error, only time you would ever install 32 bit software is if you have under 1GB of ram, like with a net book.. I actually grabbed the x64 bit of XP when it came out and was using that before vista was release
