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.