Speed wise harrier doesn't require high RPM setting to reach top speed of around 550 knots.
And you're best not to push the engine above the 102% if not necessary because if you're in that state for a specific amount of time you will damage your engine and the inboard computer will lower the maximum amount of allowed RPM to keep the JPT temps in check, hence you'll have issue landing later on.
The only difference full Throttle setting makes is the acceleration.
If you really need to gain speed quickly punch it as hard as you like but for a short period then lower it below 102% RPM.
Now depending on how long you want to fly you can use 100% rpm to reach about 500 knots then throttle down to about 50 - 60% RPM.
You can still maintain the same speed without wasting fuel.