The subharmonic generator is essentially the same as an analog octaver. I've heard people say that sub pedals like the Meatbox are a different effect to octavers, but the technology used is the same, just that they are voiced/EQ'd differently.
What I do if I want an octave up is just play an octave higher and let the pedal fill out the octave down. Sounds much better to me - instant tracking, and no fake sounding digital artifacts you get from digital octave up!