If NZ has flat beds in first, their marketing department or web site designer needs a bit of prodding. Their web site shows a fairly ordinary seat and gives the impression that it reclines fairly generously, but makes no mention of beds such as QF etc offer.

I don't know how to quantify the difference, but the "real" beds offered by several carriers are significantly nicer than even the most comfortably-reclining seat. Besides flatness you get your own private space, some kind of sheets/comforter thing, and a nice pair of airline-issue jammies you can don prior to some fairly serious sweet dreams (smooth air permitting). Given a choice, I would NEVER turn down a real bed on a long-haul (unless Aeroflot puts 'em in.)