I'm looking for a calculator/table that will tell the payback time of ANY field. I know that this tool exists for crop (among others, https://multimadness.de/cropcalcT44_extended.html) and kirilloid can tell you when to build the bonus buildings/HM for all resources. What I'm struggling with is how to develop a cropper (second village) while also upgrading the spawn. For example, should I upgrade my crop fields to 7 in cap before bringing my iron mines to 4 in the spawn?
I know I COULD do these calcs by myself, but figured I'd see if the work has been done for me.