Stumbled upon this thread by I don't know how?
My current gear: DT 990 600ohm on a Maverick D2 or NAD D 3020 or Creative Z or Fiio E09k+ E17 (totally depends on what I want to use them). Been using it for 4 years now. Might actually sell it. Past gear includes an extensively used HD 650 ( loaned from a close friend) on Essence STX, HFi 780 on an iBasso d2, Bose QC2 for starters.
Upgrading to He-400i this month. Friend is getting my blackfriday purchase home
For your suggestion:
1)What you like is more important that what you want to like.
2)For me, personally, HD 650 is a little bright on the highs, while the bass is just about enough with good extension. Mids are not great but not recessed like the 990s.
3)Comfort wise, it is more or less equal to dt 990s. I've slept listening heavy metal on both the cans for 3+ hours without sweating my ears(In Chennai it's a big deal).
4)Why I opted for He-400i is because it's better than both dt 990s and the HD 650s. Also, they are not that bright, which is my kind of cans.
More suggestions: If you are someone who loves neutral cans and doesn't mind missing on the lows hitting you deep, then HD 650 is a good bet. However, as I mentioned, I did find the highs a tad bright for my taste. It's 300 ohm and you know it requires a little effort to drive them well.
To conclude: HD 650s will go on sale during September, October before the actual black friday sale begins in the US. You'll get great deals. Another suggestion is, My friend is trying to sell off his HD 650, as he is upgrading to stereo setup.
Guess I helped you somewhere along the post
gl with your buy!