There are a lot of things that can be said about detail or resolution. I think it's helpful to separate out a few different characteristics.
The first is treble energy. There are some headphones (Shure E500, Sony MDR-SA5k) that have an awful lot of treble energy. This may lead some people to think the are detailed or resolving or clear, but this is false. It just means they have a lot of treble energy.
The second is transient definition. There are some headphones (SA5k, Sony MDR-D777) which have extreme transient definition. This causes the headphone to have very strong separation. But this isn't the same thing as resolution or detail either.
The final factor is resolution, or the ability to portray inner detail. There are some headphones that fail in the first two regards - the Grado HP1000 and Stax SR-X mk3 come to mind, but still resolve tremendous amounts of inner detail. This is where resolution is key, as it is only if a headphone can do this, that they can portray a timbre or texture that is true to the underlying recording.
So where does the SA5k fit in the grand scheme of things? It certainly is a treble happy headphone, and has the most insane separation out of any headphone I've ever owned. These things are not good things, in and of themselves. In most rigs, they're not all that detailed/resolving either - only average or below average. You need to have the right setup to bring out the resolving ability of the SA5k. But the same thing can be said of the HD650, HD600 or even K 701 I suppose.
Where the SA5k is really strong or weak is in areas other than underlying resolution, in my opinion. Strengths are that its separation is very good. Also it is punchy and has an upfront tone that is enjoyable. Weaknesses has to be with the fundamental accuracy of its timbre - there's a reason why many find its timbre to be tipped, plasticky or just not quite right. But its strengths are there - it is capable of being highly resolving. It does have insane separation. These things makes its imaging interesting, though perhaps not really holographic.
All in all though, I don't quite see why there is so much discussion/debate about these mid-level cans (SA5k, K 701). They're all enjoyable but not really all that impressive when you really have a chance to listen to many things. Put on a good K 1000 rig or SR-Lambda Pro setup or HP1000 even, much less a good Omega 2 or 010 setup, or even a HE90, and it's just that there are more interesting and impressive headphones to talk about, at least from a resolution/detail standpoint.
Best regards,
-Jason