I fully agree. I have seen hulking neutrals carrying just a few amps because the system is balanced that day. It may not be balanced tomorrow.
I am not saying that any of the proposed suggestions will not work. I am saying is giving the size of the service, it tells me that an EE did the design. It has been years since I worked in Michigan and a design over $100K (possibly local ordinance) required an EE stamp. By veering from the design basically voids the stamp just like voiding a product listing. If something to were to happen due to the change, the EE will not be resposible but whomever made and allowed the change will.
I have no clue on what the service is powering so I could or would not chime in on what size of neutral to use. For example, what kind of harmonic loads and sizes are involved? Whatever it is, it is big. I would not want to be the one to give the go ahead now to use a smaller neutral and have something go wrong with it years later because of an unknown. I would not want to be anywhere near the facility if it were to lose its neutral.
I would not have any problem using a smaller neutral if there is real value to the project, but not without the EE's blessing. I do not use reduced neutrals on a dwelling service. The cost to size it is not covered in the savings of using a smaller wire.
