Yep, speed is pretty much a constant if you want a controlled "landing". You need enough to allow the wings to take the weight of the aircraft right up to the point that the water takes over that role, but no more, since that's just extra energy to take into the crash. This sort of fully held off landing is not the way you'd normally land an airliner, but exactly how you land a glider or any other light aircraft. In that respect, actually, the Hudson landing was probably worse off as I'm guessing the aircraft was heavy, having just taken off and not having jettisoned fuel, so it would have needed more speed.
Calm water was probably the biggest factor, as with even the normal swell of an ocean it would be a challenge to land an aircraft with absolute symmetry as Sully did.Hit one engine or wingtip even milliseconds before the other and you have the Ethiopian 767.

Also, the bigger the span, the more difficult it is to keep the thing level. Ask any glider pilot that! The 777 has a distinct disadvantage over the A320 there!