As others have pointed out, OpenGL does not improve the final render. It just makes the previews look good. It should speed up the workflow, since you won't have to render to see how something looks.

You may be confused, because OpenGL really improves the look of 3D games. That's because they are always in preview mode - redrawing the scene on the fly.

It sounds like there will be some nice new render options in P6. I'll be happy if they just fix that "small scale" problem.