For those who like figures: "We have 14 district and bankruptcy courts. The 9th Circuit as a whole has 164 district judges, 131 magistrate judges, 79 bankruptcy judges, and 119 pre-trial/probation officers."
the 9th Circuit is not the largest producer of opinions. The statistics show that both the 7th and 8th Circuits consistently produce more published opinions than the 9th Circuit. If division of a circuit is justified on this basis, other circuits will have to be divided.
Reversal rates have nothing to do with circuit administrative performance. The Supreme Court may review anywhere between 13 and 25 cases a year out of the 9th Circuit's 11,000 case filings. The question of how a court would decide the merits of a handful of cases is not reflective of court administration. It is not a proper measure, under any circumstances, of whether a circuit should be structurally divided.