<< Whilst a set of pads with only 1mm of material left will work fine in normal light use start working them hard and you will soon find that they fade pretty rapidly since there is no material to dissipate the heat. >>

I don't know whether Challengers have special braking arrangements, but I don't think the amount of material in a brake-pad is great enough to 'dissipate much heat'. Pad material being a relatively poor conductor, I would also guess that when only 1mm thick, heat might reach the metal backing (and onwards) faster than when it is 6mm thick ? (Which of course, might raise the temperature of the fluid in the caliper cylinders)

But most heat will be dissipated via vented disks, which this vehicle will surely have.

I`d be more worried about pads breaking up, at that thickness they stand a good chance of breaking up, if had to do an emergency stop, used to see it often when people neglected brakes where the pad so low they hardly worked as friction material had broken up!

A few mm of thickness will make no practical difference to the temperature of the brake fluid.

Did I mention the temperature of the brake fluid?

You mentioned brake fade which nowadays only occurs on the race track, or perhaps descending an Alp with a heavy caravan. Boiling brake fluid causes it. Very hot surface brake pad material can also cause it irrespective of how thick the pad is. Indeed, with severe use it is more likely to occur with new pads yet to bed in.

Forget the physics, a pad with 1mm needs changing NOW

Agreed, apart from forgetting physics, an understanding of which is essential for fully understanding the workings of a car.

However, a 10mm thick pad has at least 8mm of use. With normal driving, front pads should last at least 40,000 miles - probably double that on the rear (e.g.my heavy Audi, still has 3-4mm after 71,000 miles). If the OP has 3mm, at 5000 miles per millimetre, he should be able to do well over 6000 more miles before they fail the MoT 1.6mm limit.

I repeat - waste not want not.