Those scratches in the bearing are from debris in the oil. How did it get there if you have a filter? Simple, the bypass opened and let unfiltered oil by. Why? Dunno, could be going too long between filter changes, could be defective or cheap filters, could of even been from poor cleaning during the build.

If you aren't seeing copper thru the babbit (the silver looking babbit material is softer than the crank so that debris will score it and not the crank)then I doubt the bearings are the low oil pressure culprit.

Out of curiosity, did anyone mention the oil pump drive? If the shaft is not pinned to the gear it could be slipping. Higher RPM's would aggravate this.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.