Measurements. Looks pretty bad, sibilant, bass bloated, limited bandwidth and high distortion. Z7 measures a lot better, though it lacks some treble extension. Maybe it measures better with a more shallow fit and vent mod, but I don't see it dethroning the EX1000 as the best Sony IEM. Or maybe the real gems are the A3 and or the A2.
Sibilant at 10 khz? OK, you took ref. plane measearuments? And do you realize you'll probably get quite a different picture given 6mm from ref. plane? Like, longer bandwidth, no 10 khz peak. And a listener will never ever be able to insert Z5 deep in his ear canal to the ref. plane without godlike surgery on his ears and skull.