[BScout]

Haven't run your exact configuration but gigabit ethernet is too slow in general.

Having done something similar though. You'll need your client computers (the one running Pro Tools) loaded with RAM and your disk cache set high enough to cache the session. That is how we worked.
Picture is still an issue though (since that does not cache.) Using DNxHD36 we were able to do it (keep picture on the SAN) but it required that the full sessions be cached into the disk cache.

(In essence, after starting/opening a session and giving it time to load to the disk cache, only the picture was actually being read off of the SAN actively.)