My personal rule is to stay between 60 and 62. However, diamonds with a depth of 63 can still have lovely performance if all the numbers are in line...
Hi Diatan - not if all the other proportions are in line (although I like lower than 63% depth because I don''t want all my weight in the depth of the stone! - his 61 or you are stepping off a cliff analogy is entirely too drastic and frankly incorrect) - there are a lot of angles in there - in a round brilliant you need good crown angles and pavillion angles, table size, etc - Cuellar''s book kinda of scares people (and in retrospect I think that may be on purpose so that you feel he is the only safe person to buy from) - Please take the time to read the tutorials section under the knowledge heading at the top of the page and hang out on PS for a while and you will get very comfortable with diamonds and be able to understand what you are doing - you will end up with an incredible stone with the knowledge you learn!
This is an interesting topic! I recently bought (thanks to PS) an enagement diamond with the following characterstics. I was a little gun shy about going over 62% depth but this diamond is an AGS 000, and in person it is incredibly beautiful and does not dissapoint in any way. It was a good price and weight and so its what I was looking for. I am very pleased with it! Its total width is a little smaller than a diamond with a 60.5 depth but its so minute it really is a non-issue, and since it is so superbly cut, it does appear larger.