I did some "unusual" testing of same lot factory made panels (all 3 types, single, poly and amorphous) a few years ago for Amanda. Then more tests later for myself.
It is not apples-to-apples.
One may do better in high humidity, or at a slight angle, than the one that does best in good clean straight sun.
The output variation could get to double digit percentages, even with a slight variation in input variables.
I did not do much testing regarding temps, though I expect it is similar.
A cabon pile tester would be roughly Isc, so just need a meter than can handle the expected Isc and test Isc under several conditions.
I go old school on this type of thing now... get some batteries at low, mid and high voltage, then see what each will put into a battery under a few different conditions. I figure that's about as good as it gets without a lab.
G-