What speaker gauge for my setup?

[pixelthis]

With most receiver based systems you can't hear wire and cable differences.

THIS is true, basically, but you still need as large a guage as you can stand, 12g is a good choice.
ITS slight, but a smaller gauge has more resistance, which will
make your amp work harder.
WHICH is also why the gauge needs to match on all channels.
Excepting ones with external amps. My left/right has a thick monster
speaker cable set, don't know the gauge. THE surrounds are
all powered by the receiver, and all the same gauge.