Question on installing gem upgrades

I have upgraded my gem watir 1.5.6 to 1.6.2 without removing 1.5.6. Do
you think it will have an impact on the scripts choosing which gem to
run? After upgrading watir the gem list shows both versions watir
(1.5.6, 1.6.2).

Also, do you think that it is possible to successfully run a script
using require watir 1.5.6 overriding the latest version if needed?

Thanks MC