I spent 6 years in hd600s for 15h a day, switched to Adam t5v recently. Soundstage differences are quite overblown by people, audiophile legacy lives strong in epithets used to describe things. I'm not saying it's not there, but it is not the most important experience changing bit, to me at least. On side note was quite surprised speakers emulate sound coming from the back just as well as headphones in games, I assume it's more about what we think we hear than what we actually hear.I've just got the HD 800S. I really like it but I was not BLOWN AWAY by the soundstage.
Difference will be minimal if EQ creates identical response, 700 and 800 driver distances are really close to each other from what I remember, it's the only difference I can think of that would influence spatial sound if FQ is the same-ish. Question is would 700 driver be able to withstand the EQ or not. Without proper rig and both headphones on hand doubt anyone can answer with certainty. isn't oratory do the Harman EQs for everything and remeasuring them? could check that, personally I really hate the sound his EQs create
They are also using 700s drivers in HD660S, but enclosure is radically different to 800s.