I''ve been looking for an ACA stone on Whiteflash and have noticed that they don''t have Gemex reports available. I always like to see them as they give you an idea of what the diamond can do under light. I particulary like to see the patterns of light that it shows.
It is my belief that at the upper ranges of high performance, Gemex does not do a great job of descrimination. It is exactly at these upper ranges that discrimination counts. No one cares if a diamond is medium or fair, but when it performs well, then those of us who have interest in this aspect want a high degree of discrimination and meaningful grading.
Maybe John from Whiteflash will also give you a reply.