I wouldn't categorize cold-rolled as "trash." The composition of the steel has far, far more to do with the "trashiness" of steel than how it's rolled. In fact, I many better grades of steel are cold-rolled, because the cold-rolling process strengthens the steel and imparts other desirable properties.
Generally, I don't think there is any 100% reliable way to tell the difference. As you note, hot rolled has a surface scale, but that can be difficult to identify if the steel is weathered.
"Stressproof" is not equivalent to drill rod. It's another thing entirely. It's a trade name of LaSalle Steel for 1145 steel that has been manufactured in a certain way. "Fatigueproof" is similar in composition, differing in the the manufacturing process.
Both of them machine very nicely -- a heck of a lot better than drill rod or any of your typical hot- or cold-rolled "mild steel."
Do a web search for "Stressproof" and you should turn up a bunch of information.
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