The point the heating and cooling system can no longer keep up with extreme temperatures can be found by calculating the temperatures that the absolute values of cooling and heating deltas equal the static indoor delta. This can help determine if a system is adequately sized for the building envelope.
There’s a bunch of other comments so go to GitHub and read them there.
I don’t think there’s anything to do here. You can already get to this data on the Temperature Profiles chart by looking for where indoor temperature delta is 0.
