Depends, for most dryers the temperature is limited because water evaporation is taking all the energy. The motor takes the same energy per time, so twice as fast actually uses less energy. However there is a limit to this, eventually (the end of the cycle) you reach the point where water isn't evaporating fast enough to use up all the input energy and temperatures go up to heating clothing fibers to no useful purpose and this is wasteful.

Also, is the dryer located in a climate-controlled part of your home? If so, the air that it exhausts will be made up in equal volume by outdoor air pulled into your living space. How much extra energy does that make your heater or AC use?

Idk about the rest but the ratio of energy used by the heater compared to the motor is greater than 10:1.

Edit: 20:1 mentioned here https://qr.ae/pGNTie

If we assume for just a moment that the time to dry clothes scales linearly with heat applied, we can try to run some numbers:

    Total power usage for full heat is (5000W + 250W) * 0.5h = 2625 Wh
    Total power usage for half heat is (2500W + 250W) * 1h = 2750 Wh

So that's a 4.6% increase in efficiency for using full heat over half heat.

So the big question remains, does lower heat dry clothes more efficiently, and if so, how much?

The Stack Overflow answer you linked raises some interesting points, but doesn't seem rigorous.

From an industry pdf I stumbled across, it looked like moisture sensing improvements were the best bet to save the most energy. Though, I didn't see anything about comparing heat settings in that doc, which may be telling.