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

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.