After seeing this thread I was perusing a pro audio website and saw this.
Approximate signal losses in speaker cable for a 100-foot amplifier-to-speaker distance at various impedances:
10 AWG: 4 Ohm = .44 dB, 8 Ohm = .22 dB, 16 Ohm = .11 dB
12 AWG: 4 Ohm = .69 dB, 8 Ohm = .35 dB, 16 Ohm = .18 dB
14 AWG: 4 Ohm = 1.07 dB, 8 Ohm = .55 dB, 16 Ohm = .28 dB
16 AWG: 4 Ohm = 1.65 dB, 8 Ohm = .86 dB, 16 Ohm = .44 dB
18 AWG: 4 Ohm = 2.49 dB, 8 Ohm = 1.33 dB, 16 Ohm = .69 dB
I didn't do any math to verify accuracy, but it seems like a reasonable enough SWAG to me.
FWIW (and I admit it's not worth much) I like AWG 12 for my speaker wire. No engineering reason at all, I just feel good about
#12 . It fits most AVR and speaker terminals and is easy to work with, readily available and if you are already paying for wire it's not to much more expensive.