it's as much a function of the load you're trying to drive as anything about the opamps intrinsic sonic character. I have 16 ohm iems, at 96dB/mw, so they take some grunt. Opamps which deliver really low amounts of current into low impedances won't sound as good as ones that will. Sometimes you can find this in the datasheets, other times, not so much. I like the sound of LT1028s, but they are very low current, iirc, and i won;t bother trying them in the Mkii at all. So far, the 627s sound very good, and i am wondering why a relatively fast opamp (the 627) has a reputation for being warm and sluggish.
I'm using low ohm and high sensitive iems/headphones too.
I don't think the datasheet could justify an op-amp's characteristics in audio performance.