I once read an article in one of my nerd magazines about a study where they took a standard reel of wire, made a bunch of HDMI cables, all of the same length, and measured them. The measurements showed that the cables varied by as much as 6 dB! Note that theses cables where made at a production house, NOT hand assembled, so what they were seeing was normal production variation.

You can control this variation by adding cost to the process or cost to the material. For example, you might make a bunch of cables, measure them and throw out the one that don't meet your specifications. This is costly in both time (to measure) and material (scrap), but it can be done.

So my expectation would be that if you spend big bucks for cables you are getting high quality components with very tight performance variation. Then you can start arguing about whether or not you can actually hear the difference that these cables make. Or whether your money is better spent on bigger issues somewhere else in your system. Where's the best bang for the buck?