[unknown321]

I've got potassium nitrate (kno3) and sugar. I seen that adding rust powder to rocket fuel makes it burn faster.

Is a rocket with fast burning fuel better or worse? Do you get more thrust?

Deciding on whether to make rust powder or not.

[Pawnhub]

Faster burn more heat energy being released, more thrust but less fuel preservation.
Slower burn will be less heat energy being released, less thrust but more fuel preservation.

Really it's up to you, maybe layer the fuel so you can have different burns at different altitudes.