Got the Z5 a few days ago and replaced the original cable with the M12SM2 from Sony. The small comply tips from the N3AP also replaced the default tips from the Z5. Like you, I have the impression that the Z5 is moving more air. I don't know if it really is the case. The highs are benefiting from a slightly better extension in my opinion. Not that the ones out of the N3AP are rolled off, but the difference is quite noticeable. Talking about the bass feeling down your neck, I understand what you mean and I agree with you. It's not a question of quantity, but a kind of an extension of it or a presence, as you said. Nice feeling.
I love the N3AP. As an electronic music enthusiast (from Ambient and Drone to pounding Dub Techno), the bass of the N3AP remains the king between the two for me. It reminds me of my LCD-X. Quantity and quality-wise perfect. I am also listening to a lot of other music styles (vocals, movie soundtracks, metal and a bit of pop) and here is the Z5 a step ahead. EQ or not.
I paid, if I remember well, approx. EUR 230 for the N3AP and USD 499 for the Z5. The wider soundstage, better tonal balance and more extended treble of the Z5 are quite expensive to justify to be honest. Problem: once you've put the super confortable Z5 in you ears and you get that 15/20% better sound with aforementioned styles, it's difficult not to admit that the extra cash hasn't been well spent (it's subjective I know).
Now, the Z5 leak more than the N3AP. So, at the office and in public transports I use the N3AP. The Z5 stays at home. For the time being...
I may have gone a bit out of topic, but "mer" was tempted by the Z5 if I am not mistaken. So, I also wanted to develop a bit, I hope you don't mind Wiz33.
(Source: FiiO X5III with A5 amp)