"G.R. Patterson III" wrote:
You could total the actual maximum current draw of the avionics
and add an appropriate safety factor, but this will be very close to
the total
of the avionics CBs anyway.

Not necessarily. The factory that built my plane wired avionics boxes
drawing less than 1A to 5A breakers. Subsequently a shop wired a
low-draw item to a 5A breaker, I guess just because there was one
unused CB already there. I would determine the total draw, before
messing around replacing wire which may not be necessary.

Fred F.