Well, the thing with BA drivers is, they always sound somehow soft. If a dynamic driver has such a peak, it is easily audible and very disturbing for those with sensitivity to high frequencies, just as your impression about the HD800 shows. For me, the k3003, which has a similar treble emphasis as the HD800 (6dB around 5k) is much easier to live with, due to this particularity of the BA drivers.
As I already said, the severity of those dips and peaks are source dependent, and Layla is very unpredictable, as many of us noticed already. You might be lucky and get away with a 4-5dB peak, which will become apparent only on bad recordings, where de-essers are not correctly applied, or where drums are too bright etc.
To me that's not really a big problem, since I eq my headphones anyway, it's what I do and I have yet to hear a pair that doesn't require that. Some food for thought: the engineers from Shure decided that an eq should be implemented in the amp of the KSE1500. Those guys are into pro audio for some time and that decision speaks volumes about the headphone segment of audio. Even that 3000$ electrostatic unit, the best IEM of 'em all, needs corrections if one wants a truly reference sounding monitor. The only disappointment was, for me, that Layla was advertised as such. But I learned to live with the fact that, to this day, there's no such thing as a truly reference headphone. You have to do it yourself.