A typical wildfire is not putting much of its overall energy output into bringing fuel up to combustion temperature, though. The combustion energy in a kilo of wood is measured in megajoules; the amount of energy needed to elevate the temperature of a kilo of wood by a degree is measured in kilojoules. So while you're right that the energy budget needed to combust new fuel goes up by 40% or so if the fuel is at -50°C, the energy budget going into that is only a percent or so fo the total energy the wildfire is putting out. The rest of the energy beyond what's needed to bring fuel up to combustion point is going into making massive walls of glowing flames, mile-high convection columns of air, sending smoke thousands of miles, etc., etc...

That is, in many ways, precisely what makes it a wildfire, rather than a smouldering ember.

In the limit - when a fire is dying out - then I guess, for sure, changing the fuel temperature can sap a larger part of the energy budget.