I think the most important questio....is why are you running 5 user accounts at one time? With 1-2 users logged in I don't think you would have this issue. Running time machine, filevault, youtube, pages you should pretty much see no lag. I would try that for a few days and see if you run into the same issues.
So if I just logout of each account when I am done then go to another account I will NOT be using extra RAM is that right?
Because I have no problem logging out.