Wow, thanks. Good infprmation served up quickly, what more could I ask for?
So let's see, food needed by city size:
I know, no surprises, but it still helps me to visualize it. Realistically you don't often have more than 5 food surplus tiles, some flood plains, some specials, some irrigated grassland farms, possible under Biology. So if you have 5 pop to work them and hurry your growth you are much better off whipping a pop 5 city than a pop 20 city in turns of regrowth. Of course a pop 5 city will feel the loss more and likely have less food sources anyway.
As for the granary, that stores 50% of food after growth, meaning you need:
Well that list is off by one spot, but you get the idea. A size 22 city needs about twice as much food as a size 5 city to grow back one pop point. That might not tell you which city to whip and when to do it, but you can take that into account when choosing whether to whip or not.
Now, by looking at your food surplus per turn you can see how long you will be unable to work your cottage(s) and what the cost would be.