Bingo!

This is the first time I had evidence that physiological changes had started to take place that allowed me to exercise more comfortably at 35degC.  Lowest running speed (at HR of 125 max) was up to 6.8kph (from 5.6) and the lowest walking speed back up to 6.4kph.

Start: 13.9C/81% humidity;   Finish 35.4C/64%

Lowest run speed 6.8kph

Lowest walk speed 6.4kph