2002: Boeing 307 Stratoliner ditches in Elliott Bay

The Stratoliner would present a rather clean profile -- nothing hanging down down to induce drag as it touches the water.

Two Boeing Stratocruisers (much larger B-29 based airliner) ditched in 1956. In one case they ditched near a picket ship. It sank 3 minutes after all occupants were rescued. In the other case the plane ditched in Puget sound & remained afloat for 15 minutes, but there were several casualties.

The 767 would have a couple large engines hanging down. Unless they separated cleanly & quickly, it might not be a very flat & stable impact.

When a Lockheed EP-3E collided with a Chinese fighter, one of their concerns in choosing between a water vs. land landing was that they didn't know how the electronics comparments attached to the underside of the plane would affect the stability & structural integrity once they hit the water. The crew opted for an emergency landing on a Chinese airfield.

It sounds like the best alternative when you don't have a runway, but it's hardly a sure thing.