Just to add a few cents from my experience.
Here's what I liked about SR850 :
- sound quality - fully acceptable. I enjoyed both communicating with my colleagues (working from home) and also watching movies, listening to music (light rock, ambient, world music, ethnic electronica) and gaming. SR850 has a pretty neutral sound.
- comfort - they were on the tight side at first but keeping them stretched on a pillow for some days helped a lot
However, I have a small head, I'm a short and skinny person. Otherwise, they were just fine for all the years. No sweating at all. However, the top band was a total grease collector and also felt too warm on my head sometimes.
- open back. I need to hear people around me. They were just good enough - not totally isolated but also not fully leaking.
The negatives:
- build quality - they have served me well for about 3 years but now they are falling apart. Essentially, almost all the plastic pieces just broke at the places around screw holes. I shouldn't ask for more, I guess, for the price I paid ($40, if I remember correctly). I see some Amazon reviews where people had them broken in a much shorter time. So, yeah, don't expect them to last. The plastic just doesn't hold, it wears out with time or something. It was weird - they worked fine for 3 years and then suddenly during the last 6 months 3 out of 4 plastic pieces broke and now the headband is loose and banging around. I guess, it's better to remove it entirely instead of keeping that ugly broken looks.
- the cord is smearing my clothes. I cleaned it with alcohol and whatnot, and still, after a few days, I always notice a dark spot on my clothes at that exact location where the cord rubs at my chest.