We have found(my opinion) that as we approach 3.750 stroke or larger,especially larger, we stay with the 400 size mains as you will give up rod jornal strength as there will be more flex because there is not enough main journal to rod journal metal contact. If we do go with 350 mains. we also go 2 inch rod journals. Of course all depends on what you plan on doing and how much CR and RPM. There really is no set answer because of intended use.
racear