I think 14gauge will handle typical runs up to 100feet plus, *and* should handle any runs in a room without a problem. Just keep away from power cords (e.g. don't run them parallel to each other) so they don't pick up any 60hz hum you would hear in the woofers.
If you're really anal, take them out of the amplifier every year, and trim off a fresh inch of bright copper.
Remember, whatever you hook up will be about 3x bigger than what is probably in your amp leading away from the final amplifier section to the back of your unit.
Even scarier, if you opened your speakers, they would *not* be 10g or 12g monsters hiding in there!
Don't believe the monster-sized-wire-hype... it is just there to sucker the money away from the ignorant of physics and electrical engineering...
The most bang for your buck is investing in a sound meter and tweaking the position of the speakers and subs in your system. That is about a $100 investment, and will get more acoustic rewards than $100,000 in magical silver wrapped/cryogenic-treated wiring. LOL (all the way to the bank).