Hi,
I don't think if you split your iscsi network on different subnet you will obtain better performance. 2 different subnet like your current configuration is sufficient.
Are you compliant with all the iSCSI best practices?
I found a good white paper on Dell MD Storage and iSCSI best practices.
http://www.dell.com/downloads/global/products/pvaul/en/powervault-md36x0i-ip-san-best-practices.pdf
Are you currently using a round robin policy for example?
Can you post, your vSwitch configuration in detail for iSCSI use.
Regards,
Julien.