I have a configuration like that. I have tested both with a dedicated (dual) NIC used only for sharing. I don't see any difference in performance between ISCSI and simple sharing in my home environment.
I have choosen simple sharing, because it's simplier to manage. One of the main problem is the backup on the file server. Because the ISCSI is a single and big VHD file, you have to backup the entire file which takes space and days (you can't mount the VHD if it is already mounted in a client OS). Added to that, if your VHD file is corrupted you take the risk to loose all your data.
So, I will say: simple sharing, dedicated NIC, deduplication (50% space saved! Important to backup, because a corrupted file chunk can belong to 1000's of files!).