Do some research on auto and motorcycle-racing, they have a tonne more info on braking and performance than us cyclists.

Don't forget that using 100% braking in spurts decreases the amount of time your rims are at elevated temperatures. Heat-transfer to the inner parts of the rim, the tube and the tyre takes time due to the distance they are away from the maximum-temp point (where the rim contacts the pads). The longer amount of time you hold the heat above ambient, the more you transfer to the tube, air and tyre. The opposite is the time the brakes are OFF, in which case, the rim & tyre transfers heat back out to the ambient air. The longer the amount of cooling time you have, the cooler your rim, tyre and tube will be.

So a table of temps might look like this on a descent with steady-state brakes versus brief spurts of maximum-braking (10-minutes time versus temp of Const versus Intermittent brake use):

Time__Const.__Intrm.
0______70F______70F
1______90F______70F
2_____110F______400F
3_____130F______200F
4_____150F______140F
5_____170F______140F
6_____190F______140F
7_____210F_____400F
8_____230F______200F
9_____250F______140F
10____270F______140F

The critical thing to remember with heat-transfers is that it's both a function of delta-T and TIME. The longer the time you spend at any elevated temperatures, the more heat is transfered. In the braking example above, the actual amount of time spent under braking is just 8-seconds at 400F with maximum-braking for the 2 corners, with 5-minutes of non-braking/cooling time afterwards versus an entire 600-seconds being baked at 300F.

Another example is to use a frying pan. Hold your hand on the inside of the pan and touch the outside of a pan to a burner on HI for 4-seconds then release for 5-minutes. Then hold it to the pan for 4-seconds then release for 5-minutes. You barely feel any heat coming through right? Now put the burner on LOW and hold your hand on the inside of the pan on the burner for 10-minutes. Big difference in how much heat makes it into your hand!

Here's the basic equation for heat-transfer rate:

The higher the delta-T, the higher the transfer-rate. Multiply (integrate) with respect to time and you get the total heat-transfered during that time-period. So if we add up the heating versus cooling times for that 10-minute downhill, we get something that looks like this:

Time___Heating___Cooling
const_____600s_____0s
inter_____8s_____592s

That's a vast difference in the amount of time you spend baking your rims with constant-braking versus how much time spent with intermittent 100% braking. The idea is to spend as much time cooling your rims as possible.