I've installed "SIEMENS SIMATIC STEP 7 v5.5 SP1 + PLCSIM v5.4 SP5 (x32+x64)" and Step7 works fine (at least I think so

Now I also need WinCC, but I have no idea which version to install.
I think the newest one would be the best, but I also need to open a project which was created with version 5.1.
Will I able to do that if I use the newest version?
I have Windows 7 x64.
Thanks for help!