The lower in F you go, the more power the receiver has to put out. That is, the power shifts from the subwoofer to the receiver, so that's a little bit of a concern, also, the more bass a small speaker plays, the more distortion.
Without seeing what the receiver is doing precisely, I suspect that 80 to 120 Hz is in a good range. In some cases you may be limited to hte smallest speaker defining the crossover. For instance, if you have really small surrounds, which MUST be set to 120, the receiver may only be able to use 1 crossover setting and will choose 120 for all speakers, even if your center is bigger.
Without seeing what the receiver is doing precisely, I suspect that 80 to 120 Hz is in a good range. In some cases you may be limited to hte smallest speaker defining the crossover. For instance, if you have really small surrounds, which MUST be set to 120, the receiver may only be able to use 1 crossover setting and will choose 120 for all speakers, even if your center is bigger.