Yours should be an AGS Excellent 1, if it's cut correctly...
Actually, the 59% table doesn't guarantee that the diamond has proportions within the range for the AGS-1 Excellent rating, it only means that the diamond has the "potential" to fall within that range of proportions... To determine the proportions rating of a diamond the crown angle and pavilion angle measurements along with the girdle thickness and culet size are also needed. Ask the seller for a Sarin or OGI proportions analysis using the AGS software settings and the proportions grade will be determined for you in the report. Make sure that the measurements of the diamond for outside diameter and depth along with the table size and total depth are within a reasonable tolerance to the measurements stated on the lab report to ensure that the Sarin or OGI machine used to obtain the additional measurements was actually calibrated and that the diamond was clean when it was measured or the results will not be accurate. Hope we're not being too technical and raining on your parade, but we wanted to clarify the fact that a proportions rating can not be determined by total depth and table measurements alone... Regardless of the proportions rating, if the diamond is beautiful to you and within the price range you are trying to stay within you should consider buying it... The best way to find "comps" for the diamond is to conduct a search for a comparable diamond via the diamond search engine here on PriceScope - as dealers, we can't post the comp for you here