The maximum voltage is where the specs are still met (assuming the specs apply over a range of supply voltages). Otherwise, it is the point where the amp begins to take damage (avalanche breakdown), which is also the absolute maximum voltage rating.
Instead of building a tester for every parameter, you might be able to identify a few parameters which vary around the maximum supply range, and test the family for that.
Probably, which parameters fail first (e.g., input voltage/current bias/offset, GBW, supply current, etc.) varies from family to family, so don't expect to be able to grade just any amp based on the same parameter(s).
Tim