It's not a simple thing that they'll hit at this temperature and not at another.
Conditioning.
There's some merit in the direction of change thing, I think. 61 or 62 being optimal, and fish turning on as you go towards that. So that theory would say that lowering from 55 to 50 would turn them off, but raising from 32 to 36 would turn them on.
That said, you can only take it so far. I'd choose to fish 55 degree water over 35 degree water regardless of the direction of change.