I wonder if the 6.85 vs. 7 mm had issues other than mm diameter. If one were brighter and better-cut, it would throw off more light around it (what I think of as my flashlight effect) and thus seem larger to the eye. From everything I''ve read, the human eye really shouldn''t be capable of distinguishing differences of less than .2 mm in size. Seriously, get out a ruler with cm marks on it. Take the 1 mm distance on that ruler (1 cm = 10 mm). Try to divide that 1 mm into 10 little lines. The width of the first pen mark should be around .5 mm (i.e., you can''t even draw a line as small as .1 mm). Try to imagine that the width of your pen line contains five little marks, and see if you could tell the difference in width of .15 mm. I really think it''s unlikely that you could discern a visible difference between the diameter of those diamonds. It may have been cut (the halo of light effect) or psychological.