im no expert, but i would strongly advise against driving hard when the diesel engine is not yet under nominal operating temp. The greatest wear on the engine is when the oil has not fully circulated. And when the engine innards are not yet expanded (due to heat).

Next, diesel engines dont have spark plugs and combustion is provided by the superheating of compressed air. Thus, a diesel which has not yet reached temperature will not combust as efficiently as one which is already heated.