First of all, I would recommend splitting all iSCSI networks into different subnets like 172.16.1.x/24, 172.16.2.x/24 and so on instead of iSCSI port binding and VLANs since all additional network layers and processing might influence storage traffic performance. These measures might offload your switch too.
Round Robin is fine. I would recommend applying maximum iops=1 adjustment https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2069356.
Jumbo frames are totally worth trying since they will significantly reduce the number of packets running through your network and might speed up everything and offload the switch too. Please note that you will need to enable those everywhere in your network meaning VMkernel on the ESX side, on the SAN side and the switch itself.
For proper benchmarking, I usually use a Windows 2012 R2 virtual machine and Diskspd https://gallery.technet.microsoft.com/DiskSpd-a-robust-storage-6cd2f223 since this tool gives the most reliable and reproducible testing results. Anyways ATTO should also show good numbers.