Would you notice a difference in size between a 5.9x5.9mm round brilliant vs a 6.1x6.1mm round brilliant diamond? What about in a three stone setting? Thanks!
When set and not next to another diamond, no way. Next to another, definitely. I can see a difference of 0.03x0.05. Found out at the jewelers yesterday... unfortunately...
You probably won't notice unless you obsess over it. Setting type (3 stone, solitaire, halo, bezel, prongs, etc), shank width, and finger size also contribute significantly to the perceived size of a diamond, and together contribute more than the 2/10 of a millimeter difference. All except the last (finger size) are pretty well in your control.