Perhaps an aside from the main thrust of the discussion is the paperclip analogy.
When you talk about running engines at high, high temperatures (as one of our learned colleagues has already mentioned) the metal bits start to creep. Now, some folks say that operating in the 2.5 minute range is not cumulative...I do NOT agree...thus the paperclip analogy, to wit, if a paperclip is flexed once, it is still good to go...twice, still good to go, but if you flex that bad boy enough times, you induce metal fatigue and 'boink' bits go flying.
A discussion with engineers at the US Naval Safety Centre many years ago yielded the idea that if you REALLY have to exceed limits, its better to just keep pulling power till you're out of danger rather than ducking in and out of the 2.5 minute range repeatedly (ie flexing the paperclip).
Anyway, just my two cents worth.
HP