I'm rebuilding a set of Infinity RSIIb speakers with external crossovers and I'm using Cardas Copper Litz wire (Teflon insulation), 17.5 gauge on the tweeters, 15.5 gauge on the mids, and 11.5 gauge on the woofers. There are a total of 8 drivers, ten inductors, nine caps and four resistors per speaker. A little harder to work with but Litz wire is said to provide better transfer of high frequencies, and since every strand is individually coated with lacquer, it will never corrode. Will be a big step up over the original wire, which is actually Monster cable that had started to turn green from oxidation (it says "Wired with Monster Cable" right on the speaker). I thought about the Duelund wire but the oiled cotton insulation turned me off - it sounds a bit messy to me, especially since the wire will be outside the speakers due to my external crossover.
There are some who feel that there are maximum gauges for each level of driver, i.e. don't use too big of a gauge on a tweeter or you will lose some of the detail.
My speaker cables are Zu Ibis, pricey but very, very detailed.