Wow, You know that the manufacturer goes through some serious effort to determine the correct oil for the engine.
What are the mfg's req oils? Maybe you should stay within that range.
I am currently using Delvac 1 in some of my diesel engines. One UOA is on it's way, so very soon I will know how the oil performs. From the looks of it, it will be a very good set of results.
Is the 5-40 viscosity range acceptable for this engine?
Chris