Ditto the above response, you aren't going to find an answer.
I hope no one has or ever will conduct an experiment on a BP to see "how hot is too hot". That would be cruel.
Just follow the general guidelines of BP heating. It doesn't matter "how hot is too hot" as long as your temps are dialed in and your thermostat probe is in the correct place.
Oh, and don't EVER use a heat rock.