The center I would judge fairly equal, I feel 6.7 is better, my wife prefers 3.5. However at the edge there is a dramatic improvement from 3.5 to 6.7. At 6.7 the tower stands out nicely from the back ground, where as 3.5 is just ok I feel. On my monitor the scans show this clearly. When considering the large fall off at full open, then at 3.5 the edges are hardly stoped down. The aperture bladles run essentially in behind parts of the barrel and hardly cut the rays.