I adore Banks, and his writing ability dwarfs nearly all other SF writers (I really can't think of a single writer that can match him - though I've yet to read anything by Gene Wolfe and I've heard great things about his prose). But I would never call him hard SF.
From his FTL by using energy from the skein behind the universe, to all the wondrous stuff the drones' and ships' fields can do, to the alterations the culture humans can do to their bodies ...etc.; he basically gives magic a SF based coat of paint, waves his hands a bit, and presents it in his setting. And that works perfectly for his books. When reading them I don't question for a second the verisimilitude of the culture universe. I just don't think that can rightly be called hard science fiction, as there is just about zero science involved.