Had a quick question for those who may know.  It's about the "render in a cube" method for speeding up rendering smaller scenes.

When I render "in a cube" it doesn't seem to speed up my renders at all.  In fact, I've removed the cube some times and my render speed has increased.  I checked the last time I got this phenomena to make sure that my lights weren't intersecting the cube at all and everything was free and clear.

Now.. the question is.. does "render in cube" mean to use the cube primative or to make a cube out of 6 individual planes or does it make any difference?