«Fast» is a synonym for extended high-frequency bandwidth. And that's not stringently associated with accuracy – which is the criterion for high resolution. Another point is the dynamic, which also may contribute to the impression of quickness.
A frequency response which increases towards the upper auditory threshold may automatically be judged as «fast» sounding... independent from accuracy. So «fast» sounding headphones may be colouring ones.
The Etymotic ER-4s are an example for really accurate transducers, which are fast in an ideal, not exaggerating manner. Responsible therefor may be the very low moving mass of the tiny membrane (low excursion x low mass = accurate transient response), which hasn't to move much air volume, and, in addition, the sound's very direct path to the eardrum without any reflexions (= multipath) from the outer ear.
Another vital criterion for quickness and accuracy is the stiffness of the membrane. The closer to a piston-like movement, the more accurate and fast the sound. But it may be difficult to go through with this concept in the case of a full-range speaker like those in headphones... Nevertheless, the sound of even «large» membranes (5 cm) is astonishingly fast. No wonder, if you compare their moving masses and excursions to those of free-field loudspeakers.
Are electrostatic headphones really superior in terms of «quickness» and resolution? I'm not so sure. I base myself on my listening experiences with different types of electrostatic and dynamic headphones. And I must say that ER-4S and HD 600 are absolutely equal to the best electrostatics I own/know in terms of resolution and quickness – the latter after some modifications, especially removing the foam pad and replacing the cable – though without sounding equally. For electrostatics have a characteristical reproduction of the treble range – not unpleasing, but slightly «technical» anyhow – which give them a fresh and clear timbre, while most of the dynamic types (except the best ones) suffer from a somewhat slow treble range, maybe additionally some resonances throughout the frequency range, which make them sound harsh or nontransparent.
Yes, of course there are clearly audible differences in quickness and resolution between different dynamic headphones.
JaZZ