Very, very simple test of terrain:
This render have only 50% detail final mesh ( when i export this mesh, have 23 mil poly

) so i use displacement and have the same resault, but use texture and simple mesh.
That looks final mesh ( all detail )
http://imageshack.com/a/img827/1451/62nf.jpg
!!!! I need help - I have disp this terrain, and for example in VUE all works ok - use ram 4gb , but in 3ds max with Indigo i create simple 256k poly terrain and add Indigo Subdivision ( max number 7, pixel threshold 4,0 , curvate 0,1 , displace error 0,1 , View dependet ON, Subdivision smoothing ON) and renderer use !!!! more RAM than i have, and i have only 50% detail !!! Strange because the same scene in VUE don't eat all my RAM.
Strange x2, because earlier i render grass scene and in this scene have 200mil poly and only 8gb ram "eat".
I now test import this terrain and render - 5mil poly - crash system ( eat all RAM, system stuck ) - what is a problem?
I don't know how set Indigo Subdivision to have 100% detail in the scene and don't have a "RAM' crash.