So, the obvious question from our end is "why did you ask us if you know so much about it?" Further, use of vertical space can take many forms. It could just as easily be empty water as full of plants-- I'm not totally sure where you're going with that. You have a vision for this tank, and we all have different ones based on what you gave us. If I had that wood, I would situate it in a similar position to the first diagram, and attach epiphytes if I needed vertical relief. A 75g is not all that tall so you won't have that much space vertically to work with anyhow. A ruler for scale might have also been nice...
I'm certainly
not trying to be a jerk, so
please don't be offended. I generally don't ask questions like this because others won't have the same perspective on the situation that I would, and certainly not the same taste. I usually prefer simple 'scapes with lots of space above the plants.
On the real, I think the reason we mostly all like #1 at first glance is because is brings our eye from the middle of the tank to the front via the long branch. Instant creation of depth.
Were I to plan on using low growing plants (which I immediately envisioned), I would certainly choose #1. Had I planned on using a ton of stems, ala Luis or the Dutch, I may have decided differently.
Anyway, that's just IMHO...
DB is on the way, btw...