Speaker cable length with monoblock amps?

Three feet/one meter is a good length so you can move things around reasonably.
The longer the cable, the more inductance, resistance, and capacitance but the difference between 2 and 3 feet is basically non-existent.  For that matter, I doubt you would hear any difference if you need to stretch it to 5 feet or 1.5 M.

The idea that speaker cables have to be a certain minimum length strikes me as an audiophile myth

+1
If that were true, we would all have hook-up wire coiled inside of our speakers.

Ok, maybe, so what is your point?

Sure Geoff, draw me a picture....draw me a pint while you are at it :-)
I miss Bob over on Audio Asylum.   I am not convinced his 5-foot cable philosophy is correct but he certainly had a sort of down home way of looking at things and a good wit.  He might have had fun with some of the current cable and fuse threads around here.  Gone too soon.

I had some of his TG Audio 5 feet long speaker cables I traded him for

Maybe he made those cables one morning after having a little too much fun with C and T the night before, or too little of his Ethiopian coffee he liked, and accidentally cut them a foot short since the TG Audio website lists speaker cables starting at 4 feet and continuing in 2-foot increments.
One of his way back posts indicates he believed his HSR speaker cables (which were a single 16 awg soft annealed solid-core silver conductor in teflon tubing) sound the same no matter the length;

"Have made some in 20' and 16' lengths, but was unable to get the wire in the hose, a compromise....There are several sets in the 12-14' range and can't tell the difference between these and a 6' set"

You were lucky to have met him.