Just a a few thoughts. I upgraded an environment with a DX80 to vSphere 5.1 some time ago and after a couple of calls, we got an updated firmware for the storage system. The DX80 - and I assume it's the same with the DX60 - did not support "Round-Robin" path policy, so make sure you read the documentation and ensure the proper path-policy is configured for the LUNs. With Eager-Zeroed disks, the disks will be filled with zeroes at creation time. If VAAI is not supported (or does not work), zeroing puts a high load on the iSCSI network, because the zeroing has to be done by the ESXi host, rather than being offloaded to the storage system.
André