My only experience with the three-class 763 in Business was ORD-SEA on a dinner flight. I picked 5C based on recommendation, but moved to 5F when the door closed as the cabin was empty so I decided to sit next to a window (clear skies so nice sunset).

5C and 5D have so much extra room even with the footrest fully extended I don't see how people can trip over you, but then clutzes are everywhere, I guess.