Firstly, have you checked that the four fans on the radiator are all actually the correct way round. There is no point having push/pull any way around if the fans are blowing in opposite directions.
Secondly, as others have said, try having the radiator fans all as intake fans (don't forget air filters for them). You could also have the upper rear fan as an intake, again, not forgetting an air filter. This would blow cool air over the other components on the MB. The 900D is such a leaky case that the used air would escape from it via all the little gaps. Another advantage of all the fans as intake, if filters are used, is that the inside of the case will suffer far less from dust ingress. You could use the money you save on air dusters to buy a room thermometer
The lower rear fan, as shown on your diagram, is just the PSU output and the air should flow into the PSU from under the case and out through the rear, having no impact on the rest of the system.
I also have a 3930K on an ASUS P9X79WS in a Caselabs Merlin case and cooled by a Corsair H80 with two Noctua NF-P12's as push/pull intake (I purchased the H80 before I purchased the Merlin otherwise I would have an H100). All other fans are also intake as described above and I get very acceptable temperatures. So I wouldn't be giving this advice if it didn't work for me. The only way you'll ever know if it works for you is to try it and see.