Overall, the HD650 reveals much more audio information consistently if you count bass and mids and low treble, and is overall the higher quality sound. The SRH940 doesn't exactly have "fake" detail but it has very very detailed highs which makes the midrange sound really nice and crisp. I liked it for its crispness, which makes it quite nice for some genres like Infected Mushroom.
Overall though versus the HD650 there's a fair amount of the music which it fails to reproduce. Coming from my HD800 (obviously not a fair comparison) the SRH940 sounds like the music just got a bunch of holes punched through it, and it's just not all "there", in addition to the overall vastly lower sound quality, resolution, detail, etc. Versus the HD650 the difference isn't so severe BUT the HD650 does still make the SRH940 sound like it has "holes" in the presentation, if that makes sense. The HD650 naturally and accurately reproduces everything without any particular spotty holes in the sound, except for a gradual treble roll-off and blurring in the 15+khz region -- its only weakness IMO. The SRH940 excels at the 10-20khz region, but suffers weird inconsistencies and faults all throughout the FR spectrum. It's hard to explain exactly, but that's about as good as I can do -- the HD650 is incredible at everything but suffers in treble without a really synergistic amp. The SRH940 is incredible with treble but suffers with everything else.
I don't recommend the SRH940 as a general purpose headphone. I understand now why some people call it a $150 headphone in the bass to mids range because of all these "holes". I think it's worth $300 possibly just for the detailed treble in some ways, but it's arguable -- it depends on how much you care about specialized treble at the expense of mediocre bass/midrange. I don't listen purely to Infected Mushroom so my HD650s proved better for most of my music. (Incidentally, an HD800 takes the best of both and improves everything yet another league beyond.)
Feel free to disregard some of this though because I'm definitely spoiled with my new HD800. Still, the HD650 vs SRH940 comparison is still valid to my ears.