If it's helpful, a quick google on your phrase "Is there a measure-able difference between some standard stranded wire and "oxygen-free" copper wire?" finds this page as the first hit
that quotes this page
that appears to give some detailed info. I don't know enough to know if the info is correct, but the relevant section is quoted below:
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What about “oxygen free” wire?
Oxygen-free copper (OFC) or Oxygen-free high thermal conductivity (OFHC) copper generally refer to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below. Perhaps, it should be more accurately called oxygen reduced copper.
C11000 is the most common copper. It is universal for electrical applications. Electrolytic-Tough-Pitch (ETP) has a minimum conductivity rating of 100% IACS and is required to be 99.9% pure. It has 0.02% to 0.04% oxygen content (typical). Most C11000 sold today will meet or exceed the 101% IACS specification. For the purposes of purity percentage, silver (Ag) content is counted as copper (Cu).
C 10200 is known as Oxygen-Free (OF). Its conductivity rating is no better than the more common C11000 grade mentioned above. However, it has a 0.001% oxygen content,
99.95% purity and minimum 100% IACS conductivity. For the purposes of purity percentage, silver (Ag) content is counted as copper (Cu).
C10100 is known as Oxygen-Free Electronic (OFE). This is a
99.99% pure copper with 0.0005% oxygen content. It achieves a minimum 101% IACS conductivity rating. Silver (Ag) here is considered an impurity in the OFE chemical specification. This copper is finished to a final form in a carefully regulated, oxygen-free environment. It is also the most expensive of the three grades.
Many owners of high-end audio and video equipment value “oxygen free” copper. Behind this demand is the belief that it will have enhanced conductivity or other electrical properties that are significantly advantageous to audio signal transmission. However, as indicated above, most C11000 common copper sold today meets or exceeds the 101% IACS conductivity and overlaps C10200 “oxygen free” that has a minimum of 100% IACS conductivity. In practice, there is no significant difference in conductivity between all three of the grades as far as audio use is concerned. It can be considered to be ordinary copper wire as far as the recommended lengths of copper wire in the table. However, for industrial use, C10100 OFE copper is valued for purity and used for such applications as plasma deposition, semiconductor manufacture and particle accelerators.