The key question, I think, is will you stop double posting to Facebook even if the growth of G+ stays the same? What if, in three months, you notice that no one is talking about G+ anymore and there is hardly any activity compared to what it was in September - will you still move forward with the "Shut out FB" idea?

I'm not trying to be rude so I hope my post doesn't come off that way. You seem to be very sure about your move away from FB and that makes me genuinely curious as to that mindset.