It appears that Symantec wants to call the new Releases - Release Updates.
So this new RU5 is being downloaded to my test environment as we speak. I had to start with my management console, stop the services, reboot then update my existing MR4MP2 version. I'll let you know how it goes. I'm going to be updating 25 users - that's all I have for testing purposes so far.
Thanks for the heads up Symantec.