HD650 is a love it or hate it headphone (I feel the classic mid-fi gods all are like this). Even saying that, I fall more in line towards loving it, simply because its luscious, velvety, rich sound is something that wouldn't ever tire me out. There is definitely better in it's price range, but they will end up being used less due to ear fatigue, or something or other. Pairing that all day smoothness with that stellar midrange, and post stretch comfort... it's definitely one of the stand out headphones for me. I just wish it wasn't so picky with amping, and more sensitive so I could use it with anything.
If I had to choose between the HD650, K701/2, DT880 as far as the legends go, the HD650 is definitely far and above towards my preferences than the K70x. The DT880 is an excellent headphone, but I feel I'd rather opt for the DT990 as my Beyer of choice instead. That leaves me with the 650 as the one I'd be happy to use for all purposes, even though it isn't the best at any one thing (though certainly master class in the vocal midrange).
Today's headphone landscape is filled with a lot more killers in mid-fi, so the 650, 880, and K70x are no longer held in the same prestige as before. I'd choose a K702 Annie as a HD650 replacement, an X2 as a DT880 replacement, though I haven't heard anything to directly replace the K701/2 as that airy, clarity focused headphone. Let's not forget the Hifiman stuff that I'm sure would trade blows and surpass these in certain aspects.