I figure if the wire resistance is < then say 1/100 of the nominal speaker impedance then I'm probably in pretty good shape (damping > 100).

So for an 8 ohm speaker 12AWG copper wire is good for about 25'. Run two in parallel for 4 ohms ... etc (easier/cheaper In most cases than getting wire below 10 AWG). So for the price of a 500' spool of 12 AWG copper speaker wire I'm in business as long as there are not too many 2-4 ohm connections to be driven.