I remember learning a great deal from the SoundOnSound article, and am now only very slightly shuddering at the fact that it was almost twenty years ago.

One interesting point that neither article seem to cover (at least based on me rapidly skimming through them just now) is: how do you know whether you're in a source/sink regime or a transmission line regime?

The answer tends to take the form of a "percentage rule": if the wavelength of the highest frequency that you care about is more than 'x' percent of the length of the cable, then you better start treating it like a transmission line. I've heard of values of 'x' ranging from just a few percent (for PCB tracks carrying logic signals) out to about 20% (for location sound recording for TV & movies, back when the recording would be to analogue reel to reel, and you might be reluctant to move the recording equipment up near the action.)