This is a feature request to use gPXE with the goal to implement iscsi. I would assume iscsi to be faster considering it would give direct block access to an image verse the overhead of the file system given with NFS. Also there is movement to utilize NAS solutions like FreeNAS. I myself an others on the FreeNAS bug tracker.
Thanks,
Bryan
This defiantly sounds like a good plan, it would be interesting to see the performance difference's between NFS and iSCSI in the initrd given the performance gains you see in virtual environments typically.