I reported that I was seeing slow echo of characters back to my terminal
emulator windows when using SSH connections between these systems. I
reported it because I thought it was possible that this behavior might
possibly be caused by substandard performance of the wireless adapters
due to lack of firmware support.
Some research I did indicated that the Intel Corporation Iris Graphics
6100 (rev 09) adapters might work better if I removed the
xserver-xorg-video-intel package from the systems so that modesetting
was handled directly by the hardware. That turns out to be correct, and
all delay in character echo from remote systems over SSH has been
eliminated.
So -- the only symptom I can now report on this bug is the fact that the
recent firmware doesn't load. Don't know what the consequences of that
-- other than the error messages -- might be.