A controlled ditching surely would give even bigger pieces (hmm, completely dependent on sea state - I guess you might control it but the sea is so bad that's largely irrelevant) - somewhere between the Ethiopian 767 and the A320 on the Hudson.
If you assume a 'successful' ditching, there would be very little actual debris - basically one really big piece (the aircraft), and some smaller pieces such as the engines and control surfaces. The engines are heavy and would sink straight away, the aircraft itself might float for an extended time (depending on the degree of damage from the ditching) but would eventually sink leaving little if any trace. The wild card would be the control surfaces that ripped off during the ditching - they are lightweight and could float indefinitely.
Which, interestingly enough, is exactly what we currently have.