What do you think about HD 650 VS HD 800 S soundwise and comfortwise? (without EQ)
I'm not solderdude, but HD800S sounds a bit different for sure. HD800 without EQ in general sucks due to the idiotic treble spike Sennheiser would never rectify (in the same way Audeze will never back off their iconic LCD series design no matter the ergonomic issues that comes with it). If you're old, then I suppose you might be able to bare it, otherwise the headphone is just too "high treble" for my tastes.
650 by comparison sounds a bit less "clear" but that's probably due to that stupid treble spike. But that's about the only difference I feel. Oh and that whole "soundstage being great" on the HD800 line rings true (though I think this is because the earcups are roomy on top of that treble spike which contributes more to this "air" feel).
Which brings me to comfort. HD650, comfort is top notch for a headphone in it's category. Most importantly the weight is no more than it needs to be, and thus stays on the head as it should. The 800 is better to me due to the wider/flatter top headband padding, on top of the whole headphone seemingly hugging your head and sides of your head better (more surface area due to the larger cups).
The HD800 without EQ is just ugh, but given that Sennheiser isn't shy about making a flagship out of plastic (seriously when will laymen move on from this notion that you can't get quality plastics in devices?) the comfort benefits greatly especially if your head isn't particularly weird or whatever. I'd legit pay the same amount of money for an HD800 with a 650 driver in it. THATS how good I think the ergonomic design is. Oh and I think it's one of the best looking headphones ever made, the only thing I think really tops it in terms of aesthetics, is Meze Empyreans, and nothing else.
The HD650 though is still comfortable, but if you're riding with bald gang like I am, wearing it for hours upon hours leaves an impermanent imprint on where it rests on the top of your head (the cushion pads are the reason). This goes away after not wearing them for a little bit. The 650 nevertheless is still one of the most comfy headphones and the fit on the head is great, allowing you to tilt your head any which way, and they won't slide or things of that nature.
I'd say if you got the money, try the HD800S, maybe you'll like it (everyone at least likes the soundstage aspect). But you can't go wrong with the 650 in the sound and comfort department either way.