Well, it's only 20 more potency for ss/bb than maim/se, right? It would be a matter of figuring out what your party is doing on that 6th or 7th GCD with no SE, and figure out if losing the 10% slashing is less than 20 potency. If it's more than you know it's better not to drop it. I could see something like if it's just you and the OT with no NIN, probably OK, but with you and OT and NIN might push it over 20 potency loss. But how do you figure that? 10% damage is not equal to 10% potency, is it?

As for fracture, I have no idea really, I just do what feels right and put it up after my double FCs, basically SE>FC>FC>Frac>SE>SE/BB depending on pacification.