I have to disagree. Why would there be an 'optimal' side to this bar? As I said, early game would favor low hunger. As one progresses with their ability to produce and desire to consume then they will adjust toward a higher metabolism. I do not see why, other than very early game, one sid eor the other is better. In fact I would think the somewhere in the middle with only a minor adjustment one way or the other would be much more optimal.
The beauty of this is that if high metabolism is too OP then the FEP mod can be increased. Likewise if the low metabolism is too OP then the buff can be decreased. The sliders do not have to be balanced against each other but rather can be balanced to reflect gameplay.
This means that sure, people could stil macro hunger at low metabolism to make their shit worth just a bit more but it seems me that the effort might be just as well spent on production with a higher metabolism.
Not everyone's production rates are going to be equal to their amount of time played. Some people may desire to be doing a lot of activities beyond producing food. The frustration of finding balance in the current setup is creating a metabolism that doesn't screw productive people out of development and yet allows less productive or nub people to still survive while managing to get some shit done.
So you say players would switch to the obvious optimal spec but I'm just failing to see which side of the slider you think is optimal and why and adjustment of effects wouldn't prevent it from being OP.