I’ve never had the 6xx or 650, but have used the 600 for at least 10 years mostly for music production. I think the consensus is the hd600 are more “honest”. The 650 adds some bass but aren’t as accurate / correct etc. The 600 might be a little bass light but are a legit reference point.
That’s my understanding at least. I get pretty good results with making music that “translates” with the 600. That’s mostly from spending a ton of time with them, but says something about their correct-ness.
I would be curious to try the 660s2, but am not going to bother any time soon.
It definitely comes into play with pretty much any “gear” related hobby, from headphones and speakers, to musical instrument gear, to making a car go faster. Guitar players spend tons of money trying to get that little extra something special in their sound.
It’s unfortunate from a few angles. 1) you spend less time enjoying the stuff that is already plenty good, instead fretting about how it could be better, researching, reading, and otherwise not doing the hobby that one claims to be so interested in. 2) it’s a big waste of money. Some people have a lot of money, but tons of people over extend themselves financially on their hobbies, for increasingly minor ‘improvements’. 3) it can feed a consumerist and elitist mindset in other areas on one’s life. If I’m so discerning about hobby x, then I must be very smart and have great taste, and will need to spend a lot of money in other stuff too.
Diminishing returns is most tangible to me with music instruments, of which I’m most familiar with guitar gear and synthesizer. Everyone Really knows that actually practicing / recording / sing writing is the most important thing to “sounding good”, but it’s a lot easier to obsess about how to spend another $200 or $2,000 and Then I’ll finally feel comfortable and actually write a song.
It’s a little less obviously dumb with headphones, but just listen to music. I know a ton of people on here use AirPods more than anything else because they are convenient and sound fine.