Worth noting that one benefit of the larger than OEM gap on an iridium plug is to get a bigger spark and more complete burn, the single electrode also helps form a better flame front - multi prong plugs get in the way, absorbing heat and are purely for long life.
The tiny electrodes help focus the charge potential allowing the spark to jump the larger gap for a given amount of energy. Gapping them down to the same as the long life platinum tipped plugs (which have larger conductors and less charge density) may reduce the benefit.
Generally been very happy with the running of the IXU 24 plugs.