Pessimists......
We seem to be talking about the worst case scenario now…an engine[s] off landing on the water. The ideal is a zero/zero landing on the back of the wave, so talking about forward speed at impact is a nonsense.
The more common occurrence would be a precautionary landing with engine[s] running, fuel, gearbox, vibration, lighting damage, your mind can imagine another bunch of things…..then in this case, inflate the floats in the hover and land.