hello everybody,
derating an engine & assumed temp method are effectively used to save on engine life duration, so you save money.
it all boils down at finding the lowest allowable t/o rpm=t/o n1, which saves the most wear & tear on the engines, which equals to money in the bank.
leaving the engine at 23.5k(b734) & assuming a very high temp approx. 60°c for example will most probably produce a lower t/o n1 than derating & then assuming a possible temp of only 49°c eg.
fuel considerations are of less importance in this case, although you will have a reduced climb thrust & reduced fuel flow as well.