Objectively, depending what web site you visit, granted, Floyd are miles behind Zep, Beatles, Elvis, Michael Jackson, Garth Brookes, The Eagles, and just about level with AC/DC, on global sales.
Dark Side is generally seen as one of the biggest selling albums in history, no problem, its epic. But they have sold jack, (in relation to being the greatest rock band ever), since The Wall.
As for influence. Impossible to quantify. Made bass guitar sexy maybe.
*Just realized you already said what I've just written
Floyd have only sold 3 million units more than AC/DC, which is a fabulous band but probably too one-dimensional to take the moniker "best of all time"
Floyd have sold about 10 million more than Springsteen, and I'll put him up there against Floyd for influence and ambition
