ideally, you want your -3db point to be right around your crossover point because your receiver will slap a 2nd order highpass and a 4th order low pass on that point.
-3 natural rolloff + -3 from the crossover give -6db for the tops. -6db from the crossover gives -6db at the crossover point for the bottom.
decreasing cab volume to about 1.25 moves the f3 to 80hz, if that is what you intend to use for a crossover point.
since you have good subs, if you have a separate crossover for the subs, you could run the mains in sealed 0.75 cubic feet "full range" and put a second order low pass on the subs, flip the polarity, and have something similar to what bag end does (which minimizes group delay, thus keeping as much sound as possible all in phase).
now that i think about it, dr. geddes also employs this same approach.