Advanced SFB/SFC uses a fractional accounting system for power management and propulsion. This is why we have size classes of ships and other units; size (i.e. mass) determines what the move cost of each unit will be using the F-CA as a base platform, utilizing a movement cost of 1. Each unit's power curve is dependent on the energy available for movement and the unit cost of movement. Larger units need more energy to move, so a Dred, for example, will have a movement cost above 1, while smaller units than a CA will have a fractional movement cost.
Once you establish what the cost of each size of unit will be, you then need to create a power curve range for each class and sub-class of unit, i.e. a War Cruiser will have a bit more power than a survey ship, even though they might be built on the same or similar hulls. Role has a lot to do with power curve. The power curve range will then determine how much warp, impulse and reactor power to assign to each ship using the speed limit of 31 as your gauge.
Say, for example, you want the average F-NCL to have 24 warp, 4 impulse and 2 reactors for a total power output of 30. If the move cost assigned to this unit is 2/3, then at speed 31 the NCL would have 9 points remaining to use for house keeping and other uses (like weapons). Say we go with SFB/SFC specs and we say that shields on this unit will cost 2 points, life support costs 1 point and active fire control is another 1 point. That leaves five points to charge weapons, tractors, transporters, shield reinforcement etc. at full speed. This may seem reasonable on paper, but play testing will tell and adjustments will then be made.