amp questions

You need to remember there are no hard and fast rules for distance and watts. You can (and ham ops often do) talk around the world with a few watts. It is even more variable when you are in a mobile. Trees, buildings, mountains and atmospheric conditions will all effect transmission distance. Also have you got good audio to drive that carrier. Lots of people hook up an amp and gie no thought to audio.

Watts extend your signal (carrier). Think of it like a water pipe. The amp can extend the length of the pipe but if you don't have the water to fill it (audio) it won't be as efficient. The most popular way to do this is with a variable power modulator mod the radio. This will allow you to start with a lower power deadkey that swings higher with modulation. This is less stressful on the amp and will prolong its life.

Of course antenna selection, height and placement all have a bearing on distance too.

All things considered, the only thing that you can be sure of is that in the exact same setup, adding watts will increase transmission distance.