Uneven speaker wire runs

Just a point of order, audio signals don't travel at anywhere near the speed of light. Only light in a vacuum travels at 300,000km/sec. Even light travels at less than this depending on anything (eg. gases) it must pass through.
The speed of an electric current is dictated by various things including resistance; lightning through air only travels at around 160,000km/hour, not even close to lightspeed.
Audio signals travel by electrons being "bumped" along through the copper or silver crystal lattice, at nothing like lightspeed.
My view would be that, if you had one 1000 foot speaker cable and one 10 foot, you would notice an obvious timing error, a delay if you like. Now, 20' versus 10' isn't quite the same degree, but the effect will still be there at a much smaller delay. I don't think I could hear such a delay, but some keen-hearing audio buffs might.

Carl, do the math. Even at the slow 160000km/hour speed of lightening, one wouldn't detect the difference in arrival (or delay) between 1000ft and 10 ft cable. Don't you just love mixing units of measure?!!

Ozzy is right, if it is for home theater you probably would not notice the tonal balance difference. Plus you could set up your pre/pro to compensate if you heard a difference. In a good two channel setup you can hear it. Especially in the vocals. Good thing that most of the vocals will come from the center channel of your HT.

Thanks for the input. I remeasured and can get by with an 18 ft. run so I decided keep the L/R mains the same. I found a chart on the Revel speaker website and this length should be fine with 11 AWG wire. Their chart gives a max length for each size wire to maintain a loop resistance of .07 ohms or less. My B&W owners manual recommends a max cable impedence of .1 ohms so I should be well within these parameters.
I can't find much info on the wire I am going to use (ViaBlue SC-4) but I was looking for a wire that addresses both high and low frequency issues for a bi-wire configuration. According to what info I have found this silver/copper hybrid should work well for my home theater setup. I also found a website that will give me a very great deal on the wire.