I know for their custom cuts, it would be a range like D-F, VVS1-VS1, etc. and they will give a price range with the final price depending on what grades the diamond fall under. If you ok with the possible range and ok to wait, then can custom cut. If you already found one in the specs you want, then no point custom cutting also cos it can vary. Their white series are all tip top in the realm of diamond cuts, so either one, you cant go wrong. Just that which option takes longer and more to your preference.