Nice to see someone doing some research.I would also suggest talking with some actual guides who field dress for a living and see what they carry.You also did not say whether you were looking to purchase a production knife, or seek out a custom maker and have one made to your specs.
I would agree 440C is a good steel and I have used it to make some saltwater fillet knives.Having said that I think you should also consider using a carbon steel such as O-1 or 1095.Both are quality steels, have good edge holding and are very tough, but easy to field sharpen.Just to throw a few more variables in your search, the blade geometry,shape and type of grind and heat treat all need to be considered as well.If I knew where you live ,I might be able to put you in touch with a custom maker, that you could visit and see how its done and discuss your proposal with him.Dave