Thats interesting... so, were you saying that even the taller strains can produce good bud if you pinch them/train them short so to speak? If thats the case, I'm getting a boner!
Autos.....no pruning is best
Super Autos....Avoid pruning if possible but will still do well with light pruning. Yes yield will reduce but as super auto has a longer life and you get same or more yield than normal autos. With a great sativa effect.
Never grown Magnum but I hear constantly good things about this strain. At least now you have some good options for the next project.