deploying adobe reader via GP

I'm familiar with deploying software in group policy from an academic standpoint but don't have much practical experience. I'd like to have my entire environment up to date with version 9.3.4, currently we are a mix of different versions from 6 to 9.*. If I deploy the .msi package to all of these machines, will it just install over the existing installs with no problem or should I deploy by upgrading the various installs we have piecemeal?