Can recall your useful posts.
About to make a year with the 5s as well and still impressed by the clarity of its headphone out. Sounds as pure as it gets.
Have listened a few times to the 6 but i find the 5s a bit better (tighter bass and bit more balanced). Out of my Westone UM3x and TDK BA200 at least.
If it was not for the 128Gb i would have not bothered in testing the 6.
I have read people claiming that the 4S has the best SQ. I have not heard of the 4S myself to be able to confirm that.
In any case, I am getting a 6+ for the 128GB storage and larger screen. Will see how it fare against the 5S for extended use.