In originally planning my own cable runs, i was informed by a friend of a friend who is a truly crazy electronics repair guy (one of those people who repairs/installs those $50,000 stereo setups for a living) . He was the one who quoted me some approximate cable gauges and lengths and i take his advice quite highly. I was also going to pick up some 14 or 16ga wire when i first bought my Onkyo receiver and i had mentioned to him my speaker choices.
For my mains, the higher gauges would be ok with the short distance but i had known that i would be getting surrounds, centre, rear centre (eventually) and that potentially long runs were necessary. This is why i opted for the 12awg, based on his recommendation, and ended up getting 10awg Ultralink just b/c it was the same price so what the hell eh?
As for the impedance issues, i can attest to those problems based on my old system. In my less-informed days, i had picked up some cheap Radio Shack 22awg speaker wire (100 feet) and used it for 25 foot runs to surround speakers (Radio Shack Minimus 7s) and 6 foot runs to 2 front 6 ohm speakers.
Needless to say my stereo protection circuitry kept turning off the system. Sound was a bit crackly (music and volume dependant) and it all cleared up when i picked up some 18awg cable. I thought it was cable quality at the time but came to realize much more about the flow of stereo power since then.
