Just my own two cents; but, I don't think there really IS a "perfect" render.  It either achieves the look and effect that you're going for or it doesn't.  To say "perfect" is to assume that there is just one standard to base things on and there really isn't.  When you take away all the techno babble that is involved in this medium; all it really is is art that we're creating on a digital canvas.  Unless you're doing commission work for some client; creating art to please the eye of anyone other than yourself (to me) is the first giant step towards failure.