300 kt it is; for single engine failure. 280kt in case of dual engine failure
Not wishing to detract from the topic, and being a Boeing man, I'd like to understand this discrepancy. A double engine failure you want to enhance the chance of a windmill start, hence maintaining high speed. A single engine failure does not need the same urgency; you may need to drift down, in which case you need to slow down to maintain altitude before descending and then deciding on the problem and next course of action.