Random thoughts...do we know the steel type and temper of both of those blades? Simple variance of hardness could account for differing performance. To really test the theory that thumbnail testing is causing a difference in performance you might have to repeat the test, but this time swap which blade you used thumbnail strokes on.

One more thing to test if you haven't, perhaps with a third razor that needs some attention - stropping between hones seemed to have a positive impact on my results.

when I do a thumb nail stroke, I usually do 5 to 10 more strokes on whatever hone I was on before moving forward just to 'get the edge back.' Which kind of has me wondering if perhaps what these things are actually doing, at least in my case, is really just enforcing what I've already done on a certain hone/level and making sure I spend an appropriate amount of time at this level or that before moving forward.