There is no "perfect" finish height. The height you choose to grow the plant is based on your environment and what your space allows.
If you have 10Ft you can probably grow 6-8ft tall plants (accounting for light height).... if you only have 3 feet, you can probably grow a 1-2foot tall plant. This is when advanced techniques like scrod, lst, fim/top come into play.
Drsalt gave you some good general guidelines.
Note the heights of your plants before flower and after flower, then if you clone you will have a better idea for your next run.
Potency has more to do with genetics and overall grow environment/conditions.