Another quick point - With the company I fly for, we often operate 747 Classics into places with very high ambient temperatures.
We've found that if you have a long enough runway we're often better off not using the autobrakes, as they kick in before you can get full reverse so they heat up quite a bit just for a couple of seconds after touchdown.
We start go get out of reverse at 80kts, so that's when the brakes would start to (effectively) come on.
With no autobrake, there's no heat-up on touchdown and we only have to gently touch the brakes at below 80kts, so they hardly heat up at all. They certainly seem to last longer if we do that.