> … copyng a 2” x length slice of the image and exporting it to make test strips......
Me too. Sometimes I copy the same strip onto multiple, slightly offset layers, each with its own different clipping-masked Curves or other adjustment layer.
JPC's wedges might work pretty good on say 4"... test strips, maybe with a more limited range of grays than from full black to full white. But I still don't much like the idea of control layers with overall gray masks.