I agree that tight screw-down connections all the way seem to be very important from my experiments. Push-on connections introduce noise and are only needed for legality and convenience. However, I do not agree that 6 foot of good cable cannot make a beneficial difference. I have tried running 30A TPC cable all the way to my components, but the result is noisy, manifesting itself in a dry grainy sound that has plenty of transient snap but sounds nothing like live music. The 6 foot of good cable does provide an improvement IMHO in that it provides a degree of conditioning that reduces the noise that you get without it. What makes a great AC cable is one that can do this job well while not limiting dynamics. The mediocre AC cables just make different compromises concerning these parameters. The implication that the only relevant electrical theory concerns resistance, and therefore expensive AC cables are only about being high guage, is too simplistic IMHO.
Best Sounding Power Cord
In recent trials with many hyper expensive power cords, I have found the following to be the best sound. As everyone knows that the power source off the wall most likely has about 40' - 80' run of 15 or 20 amp rated inside house wiring before it hits the outlet. Then it makes a mechanical connection from the out let to the power cord via a great connector like watt gate, then through very highly shielded 6' run of power cable with high gauge rated at 50 amps or so, then thorugh 15 or 20 amp IEC where it makes another mechanical connection to the source. Well try this; run the house wiring (via dedicated) directly through the wall post bypassing the outlet, and terminate direct to the 15 or 20 amp IEC with each positive, Neutral, ground isolated via teflon tube. Then heat shrink the three tubes with a very good weaved jacket and plug it in directly to your amp. When I did this, the sound was fast, clean, and no holds barred. By eliminating the outlet and feeding directly into the amp via IEC termination the sound came alive. Go figure, if you use 40' - 80' of regular house wire, what makes you think that 6' of super high gauge wire would make any difference since the power coming through the house wire is only rated at 15 - 20 amps depending on what gauge you use. Also by bypassing many mechanical connectors you also eliminate much loss of conductivity. Just spend a few bucks on the watt gate IEC and terminate directly to the wall cable. Nothing, I mean nothing even comes close and you don't have to throw away $3K or more on hyper expensive cables. Also try hard wiring the big power conditioner directly out of the wall. This makes a huge difference in many high current line conditioners like the Cinepro, or PS Audio 600 or 1200 or 2000 I'm sure. This will put many exotic high end power cord manufacture out of business, but I am sure they will have some quantum physic's explaination to argue what I have just heard in my system. Goodbye to my $3K power cord, hello electrician. A 4 dedicated 20 amp circuit anywhere in your house won't cost you more then $800 tops, unless you have a 10000 sqft mansion.