This question makes its rounds every once in a while.
One of my manuals states:
The maximum rated thrust is available at the forward stop. The EEC limits the maximum thrust according to the aircraft model. The 737-800 is designated as a CFM56-7B27 rating.
The full rated takeoff thrust for the installed engine is available at a thrust
lever position less than the forward stop. Fixed or assumed temperature
derated takeoff thrust ratings are set at thrust lever positions less than full
rated takeoff.
From reading this, 27k is available at the stops. A derate (eg. 24k) will be at a position at less than the stops.
If the plane came from Boeing with 24k engines, 24k will be all you can get at the stops. If you select a 22k derate, you can still get the 24k at the stops, but you might VMCA yourself into the ground.
Any other ideas?