Zeller is the worst of the 5 bigs. Frankly I have no idea why he is starting and he should really only get time in certain situations i.e. we need some size down low. I think he would play better getting bench minutes and would probably keep him in that sort of rotation.
I've put on here a number of times that I would do something like this (I can't remember exactly how I had the minutes divided up)
PF - Sullinger 10, Lee 22, Olynyk 16
C - Johnson 24, Sullinger 15, Zeller 9
I think something like that would be the right mix and Sully and Amir are the two best players and both should be starting. If someone is playing great you give that person more time. If we need shooting maybe you leave Sully and KO on the floor longer. Maybe Lee is doing well in the interior scoring. Maybe we need Johnson's defense or Zeller's size. I don't think you have it be rigid, but over the course of a season (and if all are healthy) I think something like that is the right mix.