Shadow of Mordor- VRAM usage?

[Sacrifice]

I've just got around to playing this game. And the VRAM usage seems weird. Even just with textures on high on my 290's at 1080p, (other settings in spoiler) I'm getting near or over 6gb VRAM usage. 3 questions really.

1. How can AB report I'm using more VRAM than actually exists?
2. Are there any settings other than the texture quality that should cause my VRAM to be this high?
3. My FPS seems maxed out at the 100 cap, with no real dips as of yet, so should I stop worrying? - What are the consequences of running out of VRAM in games in general, as well as this one?

Any answers much appreciated.

Spoiler

Lighting- High
Mesh Quality- Ultra
Motion Blur/AA- FXAA only
Shadows- Ultra
Texture Filtering- Ultra
Texture Quality- High
Ambient Occlusion- High
Vegetation Range- Ultra

No DOF,
Yes - Order Independent Transparency
Yes- Tesselation

 

[pgi947]

With crossfire, half the reported vram usage to get the real usage, if it says 6gb used, it's actually using 3gb.