Just wanted to jump in and add another + for iSCSI.
Regarding windows servers, if you are running Hyper-V, you have to have an iscsi target to store VM's on network storage.(apparently you can do this with SMB3.0+ but I have not been able to make it work..)
My physical HV server does not have large drives. I would like to store my non-resource hungry VM's on my unraid server.
Connected via 10GBe should have no issues with speed.