Cryongenically treated in-wall AC power wire

$20/foot is really steep -- one of the best in wall cables is JPS and that's $30/foot but this stuff really adds up with the long lengths most residential AC systems require. I used JPS in a prior installation but it's a bear to work with being 10AWG
https://www.thecableco.com/power-ac-in-wall-power-cord-bulk.html

Much cheaper is Synergistic Research Quantum Tunneled Romex (as I recall I paid less than $500 for a full reel) -- enquire of your favorite SR dealer and they can get it for you

As to whether these cables make a difference it's obviously next to impossible to do a real A:B but if you're doing a new in wall set up for the modest cost of the SR level solution it hardly seems worth skimping

I have experience with a friend going through different steps of upgrading his dedicated lines. These lines were not very long, approximately 20 feet. There was a definite improvement going from 12 gauge to 10 gauge, and also an improvement going from basic 10-2 w/g  Romex to cryo'd 10-2 w/g Romex. 

$20/foot seems extremely high. He purchased the cryo'd Romex from VH Audio for $2.99/foot.

Shouldn’t the in-wall wire length depend on room layout and placement of your gear? What length will you need to feed the receptacles that will power your gear? Incidentally, I’d suggest 3 or at least 2 dedicated lines for your audio gear.

Several good suggestions here, guys.  To add a couple of suggestions and to summarize the good ideas that have been presented at this interim:

This is your best chance to optimize the crucial power and grounds supplying your high end system.  What you invest now will be relatively minimal in expense compared to what many of us pay for the other equipment in our systems.  Don't skimp now and regret it later.  Everything matters.  Consider the extra expense of having your electrician run the power lines in conductive (and grounded) electrical conduit.  This will provide excellent shielding for the lines and result in better sound.

Have the electrician use the top (or upper most) breaker positions in the breaker box for the dedicated lines.  This will result in better sound.  Use high quality breakers.

Go ahead and spring for the deep cryogenically treated 10AWG conductors, presuming your receptacles will accept 10 gauge.  You will never regret it.

Employ lengths that are of the practical lengths that suit your planned equipment placements while being minimal lengths.  Think of power lines and power grounds as antennas to electrical noise - the bigger the antenna the more noise absorbed.  So the shorter the length the better the sound.

Consider a minimum of three separate dedicated lines.  A separate line for digital sources, one for analog / low power equipment, and one for high power equipment or even a separate dedicated line for each mono block power amplifier if you have high power or Class A mono blocks.

Now this is very crucial and underrated by too many music lovers.  Consider having your electrician install one or more separate dedicated copper grounding rods for your high end system.  Again, separate grounds dedicated just for your digital gear.  Dealing with the amount of electrical noise pollution present on our common house wiring ground system is unrecognized by the vast majority of listeners.  Isolating your high end equipment grounding from being fed the noise present in your house wiring grounds will very richly reward you.

vtech2000

 Consider having your electrician install one or more separate dedicated copper grounding rods for your high end system.  Again, separate grounds dedicated just for your digital gear.

This is in violation of the NEC and potentially hazardous. All grounds must be bonded together at the service panel.