This business of farm rendering is not all that straight forwards....  Like you said just settings can effect the render time significantly....   You should have gotten much better time breaking the bulk by 1/6th....    Yet it does not work that way...  Perhaps it is what you suggested.. better network and distribution software...

 Why don't you get in touch with one of those pro render farm places and ask what they use..  you never know what they are willing to tell you...   If I had the money I would venture to organize a search party for the better render farm with you....  I feel the I/O hardware is also a key....  these computers are made to work with thses huge OSs...  Perhaps special boards, more compact and less clutter between the   input - Ram - PU - output

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