Question following up on the remark "Do you need FP64? If so, right now the OG GTX Titan is the default choice" I am purely after FP64 performance for scientif

Question following up on the remark "Do you need FP64? If so, right now the OG GTX Titan is the default choice" I am purely after FP64 performance for scientific compute. a) what does the "OG" stand for? b) what about the titan black model? seems to offer yet a bit more FP64 performance than the normal Titan?