Musicality:
RE272 >>>>>>>>>>>>>>>>>>>>>> ER-4S
Agreed, but this one is totally subjective.
Imaging/layering/seperation+soundspace:
ER-4S >>>>>> RE272 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> RE0
I agree that ER4S has better separation than the RE272, but I totally disagree with pretty much everything else here. RE0 IMO has better separation than the RE272 and is very close to the ER4S in this regard. RE0 is also very close to RE272 in imaging and I sometimes prefer RE0 over RE272 for imaging. RE272 has a more realistic sense of space, better layering with better depth than the ER4S IMO. ER4S sounds too flat by comparison, with little depth and little layering, but great separation indeed.
Openness and crystal clear highs:
ER-4S >>>>> RE272
I think RE272 has better highs than the ER4S - cleaner and smoother/more delicate with similar or even better detail resolution.
Vocals:
RE272 >>>>>> ER-4S
Agreed, although Etymotics are also really excellent with vocals.
Attack and Decay:
ER-4S >>>>>>>>>>>>> RE272
Umm, I think RE272 also has very nice, quick, clean decay. I actually think ER4 decays sounds too quickly, ending up sounding somewhat schematic/castrated.
Emotion:
RE272 > CK10 >>>> ER-4S
Agreed. ER4S sounds too dry and thin by comparison.
Aenemia:
RE272 >>>>>>>>>>>>>>>>>>> ER-4S
Yep, ER4 also has less bass to my ears. Or, more precisely, less bass body/fullness.
Stridency:
ER-4S >>>>>>> RE272
Are you serious?! I think RE272 sounds quite a bit smoother than Etymotics and is certainly less prone to sibilance to these ears.
Sibilance:
ER-4S >> RE272
I hardly heard any sibilance at all from RE272. Heard quite a bit more from ER4S, while the ER4P was unbearably harsh to my ears in the treble with a lot of music.