I recabled my HD800s and can report a) the effect was easily measurable; and b) the new cable transformed my listening pleasure.
In terms of measurement - the new cable is five feet longer than the old cable.
In terms of enjoyment - I can now listen from my favorite sofa.
Seriously, after more than 40 years in this hobby, I know for sure that cables sound different - even though I really don't want them to. I'm pretty much a plug-and-play type of guy, and I always hope against hope I can just leave things alone. But there is a difference. It's tiny though - as many posters here have said, it's the last tiny micro-percentage.
IME engineers are impatient because just inventing and manufacturing domestic replay systems is such a massive, towering technical achievement that they're reluctant to see the trees for the forest.
Also IME, cable enthusiasts do themselves no favors by their exaggerations - "night and day, massive change ... " which leads one to expect such huge, obvious differences to be readily detectable under DB conditions, which they aren't, because they're not massive, huge changes in the first place.
So, IME, it makes sense to get well-made aftermarket items if they have durability, physical utility, and a sense of sonic improvement. Just accept that the sonic improvement will be very slight and very subtle.