[towledev]

As a kid, I dreamed of doing this. Some of my earliest googling was related to rocket fuel, probably right after October Sky came out.

What differentiates High-Power from the other options?

[hermitcrab]

Model rockets are classified as 'high power' above a certain impulse. In places like the UK and US you are expected to gradually work your way up from low impulse motors (A,B,C) to high impulse motors (J,K,L+).