But really here is the thing, I normally like headphones that are close to the diffuse field target curve. it gives a more "livelike sound presentation", where the free field target curve is more a “ good speakers at home " sound. ( A very short summary, go down the internet rabbit hole if you want to know more)
But does that mean I think every thing else is bad, or crappy? No, and I respect that other people may like headphones, that are tuned differently.
And when it comes to the discussion about HD650 to HD660s, and you what to make a comparison as to what is better, then I'd start by asking what is your target curve or you preferred sound? Comparing like to like so to say.
Now, Sennheiser has with the HD660s made a move to target the "mobile audiofphile" marked, using a 150 ohm driver instead of a 300, and that has it's compromises. Just as Beye with it's T1 gen 3. But seeing as Sennheiser has sold to Sonova, the HD660s will likely be the last good headphone we will see in a long time. Just look at the HD8XX... But that's another rant...
