60 core performance with 9.3

I have a nice toy to play with: Dell R920 with 60 cores and 1TB ram [1].

The context is the current machine in use by the customer is a 32 core
one, and due to growth we are looking at something larger (hence 60 cores).

Some initial tests show similar pgbench read only performance to what
Robert found here
http://rhaas.blogspot.co.nz/2012/04/did-i-say-32-cores-how-about-64.html
(actually a bit quicker around 400000 tps).

However doing a mixed read-write workload is getting results the same or
only marginally quicker than the 32 core machine - particularly at
higher number of clients (e.g 200 - 500). I have yet to break out the
perf toolset, but I'm wondering if any folk has compared 32 and 60 (or
64) core read write pgbench performance?

regards

Mark

[1] Details:

4x E7-4890 15 cores each.
1 TB ram
16x Toshiba PX02SS SATA SSD
4x Samsung NVMe XS1715 PCIe SSD

Ubuntu 14.04  (Linux 3.13)