That said,I completely agree with John.T in that a derate is tantamount to an engine change with a lower max power.Therefore,firewalling the engines ON TAKE OFF ROLL,having used assumed temp+derate would only give me max derate power...
That might be true for the 777, as the 737 was mixed in here before, it is not true on that type. Max rated thrust is available with a second TOGA click or simply firewalling the thrust levers, which leads to the sound advice to not touch them in case of an engine failure past V1 especially at low weights or V1s (which can be below 100kts).