Nice post tabby. I've got to agree with frank and what was in the "opamp wars." But, one must accept that there are some instances and some pedals that the chip used makes a huge difference. For instance, using a tl071/72 in a fuzz box will typically not get you the kind of nasty fuzz your looking for, case in point then opamp big muff NEEDS a 741 and 4558 to sound right. There are others, but keep in mind that this info focused on the tubescreamer, which is one of the most copied pedal that people fall prey to for bs. I wonder how accepting people will be since we know that the capacitor argue end was settled with science.
Side note, i do believe there is an audible difference between older can packages compared to the plastic ones. I've got a bunch of NOS 70's lm308 chips, both can and plastic and the metal cans. The cans are much smoother sounding and seem to have more gain to them. I've had people blind test them, marked a & b, and people said the same things about the metal can chip, not knowing there was a difference. I also happen to have similar feelings about can vs plastic case transistors. But, I think it all comes down to the frequency response of the transistors, so it makes me wonder if there is a difference in frequency response with the IC.