I sort of agree. However, the orifice does not tell the full story. Restricting a length of tube or hose based on a fitting restriction at one end means more friction in the line, so length does play a part. I think the real question is "how big" is the ID of the original 5/16 steel? I'd think that and no4 or maybe no5 line would be pretty close.
Hose is not all the same, either. In the "hydraulics" world I came from, we used a common single braid line for med pressure stuff everybody locally called "Aeroquip." I realize that's a brand and not a TYPE. That line, for no5, example, was .25 ID. But common 2 braid high pressure hose is "true dia" IE no4 hose is 1/4 ID