Quote - I know ab't the checkbox in the item Properties tag... OTOH, I never knew you were converting it into a pure NURBS object - is that what you're truly doing with it?

REYES renderers dont actually render polygons, they render what are called bicubic patches. By default FF renders these patches at a rez of 0, ie the cage mesh which is identical to the polygons in your scene. However all REYES renderers can render these patches at increasing levels of subdivision as well. When you enable the 'smooth' option, FF simply raises the subdivision level and you get a smooth mesh. This is also why 'smooth' does not have a large render hit, since bicubic patches are inherently smooth to begin with.

(This is a guess based on experience with REYES apps, but it's probably accurate in FF as well.)