You are not regarding "in-game fatigue" at all then.
In the case of your 30-33 DUR, if you set his PC high enough to get "a full workload in a 5-man rotation", you still will have "in game fatigue" which will diminish performance.
The 100 PC is fine. You just have to move him up in the rotation sometimes, whereas you may need to move the 17-20 DUR guy down.
To paraphrase booger's 2nd post: There's the easy way, which allows you to "set it and forget it" or the other way, which maximizes the effective innings but requires juggling the staff much more often.