Moving up question

[dj32]

I posted this in the official moving up thread, but I'm guessing not many folks are reading that thread at this point...

I'm following the 100 buy in rule and moving up accordingly. Not that I'm planning for a bad run, but at what point do you drop back down if you're losing at the new level? i.e. how many buy-ins should I let go, before I think about dropping back down?