Thanks Guys.
@ Dune: I am making an effort to keep the poly's as low as possible and surprisingly I am. The quality of the texture and displacement maps is the key. However the map sizes will me rather large, around 1280 x 1280 as an example, much larger than what we have seen in the past from Xfrog trees. The kicker is when I get the Magnolia covered in leaves. This will be the moment of truth.
Note: Here is a screen capture of the ploy count (22,296) in ZBrush. This is about the subdivide detail level I use for export as an .obj for use in Terragen.