Just as a point of reference:
All other variables being exactly the same; to have something play twice as loud as a 200 watt amplifier, you would need 2000 watts (not 400). Just for you to note that 100 more watts from 200 is not a lot.
You might notice more refinement, dynamics, and less distortion, because the 300 watt amp does not have to work as hard to drive the speakers. You probably would not really notice more volume.
All other variables being exactly the same; to have something play twice as loud as a 200 watt amplifier, you would need 2000 watts (not 400). Just for you to note that 100 more watts from 200 is not a lot.
You might notice more refinement, dynamics, and less distortion, because the 300 watt amp does not have to work as hard to drive the speakers. You probably would not really notice more volume.