You could add more thrust but the airline won't use it. Your Gold Coast Singapore flight was about half the -9's range so the 125 tonne fuel tanks were probably just a bit more than half full. So even full of PAX I doubt it was anywhere close to a max weight TO.
It's fairly rare to go full thrust down the runway. You said it took all the runway to takeoff. That is the bean counter's goal. To use just enough thrust to get off the runway. A higher thrust means a hotter engine and that's not good for engine life. On the 747-8 (same engines if they're GE) we're adding power for climb, the TO thrust setting is less than the climb thrust setting.
On a twin engine airplane the plane has to meet certain climb performance numbers on one engine. So having two engines at full climb thrust is overkill. It becomes a calculus problem of having higher temps and a higher fuel flow for a shorter time. Most of the time you end up with the power way back but it saves fuel and that's what the company wants. So I'm betting your TO and climb were de-rated back to the minimum to meet the performance requirements.
Last edited by MarkerInbound; 21st May 2015 at 05:06.