lot'sa difference, but you could make a button-hole argument for either one. Just after having spent an expensive trip thru the top shelf Grado's, Senn's, and AKG's, i'll spew a personal opinion...
Grado's... these are slamming straight into your cranium, if you have the right stimulants and the correct tunes, who's to argue?... enough said.
the 650's... lot'sa talk on this one... my litmus test was Floyd... as in pink... just yummy and silky smooth... but damn... those bottom ends don't seem to come outside the bricks... but, really... relax... don't pay attention to that talk... we know what's what... lay back and we'll feed you the best... hold on... wait a sec...
I want everything this HP has to offer, but with the bottom end of the Grado's... if it had that, this thing sits on top of the magic mountain.
701's... lean waaay back... really... I mean it... grab a pair of left and right... bring down a pair of your best speakers over the top and you'll be close... (they ain't Stax... but Stax is off topic for this discussion)... we've got top, bottom, and a whole bunch in between... listen to that... hmmm.... quite good isn't it? Now you really can relax... everything is as we said... nothing more... nothing less... just lean back.
as the thoughts above describe... you need lot's of sweet juice to make either work... you ain't got it?... get Grado's.