Wilhelm Kempff played it in 4:29. Helene Grimaud played it in 5:58. Both are great artists, both are very different interpretations. I actually prefer it on the slower side, especially for the tender opening theme.
all of the debate here really reminds me of an episode from "Conversations with Glenn Gould," which is a great little book btw:
J Cott: I wanted to ask about the famous red herring that almost anyone who doesn't like your playing immediately uses against you--the question of tempo. To me, it seems that the emotional content and structural form of a piece isn't so much determined byh a fast or slow tempo, but rather that, in a qualitative sense, whatever tempo you choose creates, within that tempo field, a certain level of tensions and relationships. So that the tempo appears, in a way, like a container into which a liquid is poured.
G. Gould: I couldn't agree more and can't begin to top that in terms of expressing it so well. The best example of that, if we talk about just the classical literature, is Artur Schnabel. I think that Schnabel, and I'm not exactly saying anything new, was probably the greatest Beethoven player who ever lived. I find myself more genuinely drawn to the essence of Beethoven in Schnabel than I ever have been by anybody. I mean, you may not particularly care for the way he did certain things, but by God, he knew what he was doing... (he explains a number of aspects of Schnabel's playing)
Yes, I agree with you about tempo, I've never understood why it's such a big deal, you know. It's always seemed that tempo is a function of so many relatively extraneous things. For instance, my tempi have noticeably slowed down in the last year, because I'm playing on a piano newly rebuilt, which eventually will assume the characteristics that it had before, I hope and pray, but which at the moment has a heavier action...
keep up the good work--I enjoyed your brahms, and I'd like to hear more of it!