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

It goes back to cable manufaturars, mostly provide no relevant data! to sales and the users. None will answer this!
Whay do you think that you own now the optimal cable to your setup?
I think I've figured it out. 

0 guage (AWG) wires are difficult to work with. They are thick. Too thick to solder, as by the time the tin melts, the isolator also gets burned. It is no longer as good for isloating, it exposes the cooper to oxidize and look bad. The cable itself can not fit into any banana plug on the market. An agent must be connected between the two.
A 0 AWG cable is more costly than a 14 AWG, more heavy and less flexible. However, all can be overcome with some technology. Even up to 4 times 0 AWG!
Most cables on the market (regardless of price factor) are not getting thicker than 14 AWG. For this reason.
Some would look thick, but hey are looking so because a thick isolating tube over a regular 12-14 AWG cooper core.
Some make thick cable, but charge a lot for them. This might not be a problem, for others who spend that much on a power cable, that really makes no sense at all.
The market, as for what it is, is tricky. None tels you what their cable is good for (DF, Rc, or other), a lot of urban legends are sticked to them (cryogenic, cooper purity, high end banana plugs!) and a nylone sleve that looks nice, to cover the poor materials beneath.
Price: What would you think a 0 AWG, 2.5m (8’) long speaker cable set should cost? (if guage goes thicker or cable longer, it would naturally cost more).

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All qualities they say they give the cables: Cooper purity, use of silver, cryogenic treatment, Bi Wire, Burn In etc’ - has nothing to do with the spec. of a speaker cable. It’s all snake oil mambo jumbo, to cover their and customers ignorance.
I'll ask you a second time: If you don't care for the data being provided by cable manufacturers, what data is it that you seek?