I would think it differs a bit between different models.
With the more powerful engines(300hp) and for example no deicing boots it should have more margins then with the 260hp engines.
I only have flown BN2A-21 w/ 300hp engines, so just a guestimate above.
Anyway, it feels really safe due to being fully controllable w critical engine inoperative at stall speed.
If I recall it correctly there was a bad crash just after take of (quite some years since now) when both engines was supplied with watermixed fuel. If I remember it right there was water in both fuel thanks that came in the fuel lines after rotation (due to the nose hig attitude).