"*Trying to compare mental ray to Vues renderer is an unfair comparison."

Then your comparison to another unnamed renderer is fair?  I'm not sure where the logic is in that one...

"I am rendering out 400 frames at high quality in another 3D application in about 1.5 hrs."

*That's less than 1/4 minute per frame.  Obviously not a very complex scene.  Why it took 2 days in Vue is anyone's guess.  Perhaps you are using a Mac or some type of hardware that isn't optimal for raytacing?

*"...not fair to say Vue can render out billions of polygons and mental ray cannot..."

*Mental ray cannot, short of having 16+ GB of RAM.  Mental ray chokes on 1 million polys with 2GB of RAM.  And the landscape (terrain) objects are the hi-poly displacement objects in Vue, not the Ecosystem instances.  Those aren't instanced terrains, they are displacement objects.  I have no problem pushing 2 billion polys through Vue in mere seconds, or minutes at high quality.  This is due to BSP optimization, more than anything, of course.  If I export said terrains to Maya, there's no chance  mental ray would render them.

But I mostly just wanted to point out the differences between Realtime (Crysis) and raytracing...  I think that point was pretty clear?