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

Why would I get lost over and over agin, waist my time and money, rather that use a GPS nav device or a map, and get there first time on spot?
For the un of it...
As for the optimum, as I assume you already own an amplifier and a set of speakers, they are given. so is placment that requires the length.
You may never know if your preference is right, till you get to hear the optimum (the one) and compar.
Other cables: if I use XLR's and an ordinary catle power cord, I'm good. 
It won't get any better than that.

On top, it dosn't alter my opening line:
No one actually knows how to lculate what speaker cable they need

What you say, when I'll here it, I'll know it is. Till than, just going in circles, spending money and enjoy the journy. Hope you are not on the same page on other subjects, as health.

What does "iculate" mean?  Do you mean "articulate"?

Hmmm, I thought it was calculate, but see your point.  Always glad to see your posts, BTW.

I would edit the title of your post if possible. It makes no sense at all.