Hey Littleb,
I'll tell you... at MusicPlayers.com we take product testing extremely seriously. In fact we're the only MI publication that takes a labs-based approach to testing music gear -- something I learned back when I was a senior technology analyst at Ziff-Davis/PC Week Magazine years ago. But let me tell you about the one nightmare test scenario: testing cables!!!
We were going to do a cable shootout test of our own a few years ago, and started the process. Here's the thing:
With name-brand cables, all of them in short lengths, like jumper cables, wiring in a rack, etc. will sound great. Where you'll hear the differences is primarily in instrument cable lengths. And the longer your cable, the more susceptible it would be to interference and signal attenuation, so for highlighting differences, it's easier with longer cables. That said, some companies make them 15', some 20', some 25', some 22'... we couldn't truly compare apples to apples, and ultimately abandoned the testing.
Now if I wired up a 12 inch cable, one of Planet Waves, one Lava, one George L's (silver jack plugs or the gold ones? and which wire type as they have two?)... what would we hear? I don't think we'd hear much of a difference, and would have to record a wide range of samples of clean and overdriven tones to compare. And then, none would be better or worse than the other... they'd just MAYBE sound very slightly different eq-wise, which wouldn't matter as you could just tweak your amp settings to taste as you do in the real world.
If we compared to really cheap cables, those would (historically, for sure) sound appreciably noisy by comparison to any of the premium cables, but really, we can't see a compelling difference that makes one cable sound better or worse than the other. Truly, the best cable is the one that colors your sound the least. Cable should not change your tone -- that's for your amp and effects to do. But when a cable brings out higher frequencies better and that new guitar cable suddenly makes your rig seem to sound better... I see that as a fundamental problem. I don't want the randomness of different cables changing my tone, just like I don't care for open-back cabinets since the tone changes based on the size of the room, proximity to a wall, the material on that wall, etc...
I've read some cable roundup reviews and find them interesting, but ultimately not objective enough for us to do a formal comparative review. If someone comes up with a good test, though... I'd be interested in checking that out.