No one actually knows how to lculate what speaker cable they need

This is the oddest thread. 

Amps: Manley NEO 250 monoblocks
Speakers: Thiel CS2.4

I have correct speaker cables, for me, when I hear more than I've heard before and didn't spend an arm and a leg to do so. Plus, the overall balance and stage are "just right." 

Berning Quadrature, TAD Ref1, MIT Oracle 2M. How’d I do?

I needed a 24-foot run from my Bryston 4BSST2 amplifier to my Thiel 2.7 speakers. (4 ohm,  down to 2.6 ohm @ 160 cps.)

I chose Belden 5T00UP 10 gage cables. (1.03 ohm resistance /1000  feet; 26pF capacitance per foot)

Blue Jeans Cable made them up for me, with ultrasonic welded spades for termination. 

Couldn't be happier. Excellent bass, midrange and treble for my classical music CDs. 

Disclaimer: I'm a retired electrical engineer.