I think you got it right: "To me, it all seems to be a bunch of shooting in the dark, hoping for the best result." Well said.

For shielded cable: many folks use RG-174 as it's easily available and inexpensive. I prefer RG316 as it uses PTFE as the dielectric, and is better suited for high temp applications (like my soldering iron and our SET amps). PTFE tubing comes in any number of diameters; when I purchase mine, I normally get "20ga" tubing, as that will fit all but the largest components I use. Both RG316 and PTFE tubing are easily available on ePay and many other outlets, at least here in North America.

Thank you! And it makes sense, too.