The circuitry is a K type thermocouple isolated from the 24 volts of the iron. If more power is forced through the iron by increasing the transformer voltage, wouldn't this mean more power dissipated at the iron and therefore a higher temperature rise in a shorter period of time?

[t:temp, T:time, m:mass, c:specific heat capacity, E:energy, P:Power]

(E = mc?t) => E/T = mc*(?t)/T => P = mc*(?t)/T

According to the equation above, a higher energy input per second will result in a higher temperature rise for a given time, since the mass of the iron and the specific heat capacity of its material are constants.