I'll give you $100 if you can consistently identify, in a double blind sample, the difference between monster cables, Purist Audio Dominus, and zip cords.
Let's face it, even THIS is marketing bunk, and has already been disproven in actually testing such as what I suggest. Beside my $100 there was also a standing $10K guarantee of the exact same thing. The offeree escapes me at the moment, but I'm sure I can find it if you want to take them up on it.
Lastly, there is a tiny amount of truth to the myth that size matters in speaker cables: To the extent that your speaker cord is small enough to cause a significant voltage drop, there will be an audible difference. For all but the longest runs, or highest powers, however, the resistance of the cable, when taken in combination with the resistance of the speaker, is negligible and inaudible. Remember, even in a "large" resistance cable (such as 22 gauge zip cord) the difference your amplifier "sees", and thus what you hear, is still relative to the 8 ohm value of the speaker it is driving, and thus what you are claiming to hear is the difference between 8.05 ohm and 8 ohm...
If I spent $5K on speaker cables they must be good and clearly there is a difference - why else would I spend $5K, right? If only the physics supported the marketing...
Doug