Being a passive component, the overload ratings are given by the thermal losses. Which in turn are given by the core and copper losses. You can estimate those via the core losses plot provided by the core manufacturer, plus I2R copper losses.
To validate those estimates, you have to perform experiments, and measure the average wire temperature via the cold vs hot resistance method.
However, since the internal layers always run hotter than the external layers (for obvious reasons), the best method is to insert a temperature sensor on the inner layer and read the actual temperature.
Ultimately, the insulation's thermal rating is what will be the limiting factor.