Yep yep, the OCC part only covers the casting of the metal from bar stock into the wire, if the bar stock has, for example, high amounts of contamination and has 5% lead or something in it, that's going to carry through. So usually places like Furutech or Acrolink will buy a high purity stock (in terms of not having metals impurities) from a place like Nikko or Mitsubishi, so they have a good starting point. The OCC process does force out a lot of the oxygen because when you heat anything (like water, when heated, starts to deplete in oxygen - this is part of the way that we degas solutions and make them anaerobic in the lab I work in) oxygen is going to leave - and then if you do it in a nitrogen environment as is typical when working with metals that easily oxidize like copper - then you end up with a metal that has very little oxygen in it. However, you of course could make an OCC copper that is not ultra pure, if you wanted to. Then, OCC also makes it so that the molten copper or silver crystallizes into 100m long crystals because that is how long these massive molds are, vs cold extrusion of the wire where the crystals are going to be there. It does make the metal physically a bit stronger, this may be why there are industrial applications for OCC outside of audio, not an expert on that sort of thing though.
http://www.amazon.com/Solidification-Separation-Theory-Practical-Applications/dp/3540182330/ref=tmm_pap_title_0?ie=UTF8&qid=1311787626&sr=8-1
I really need to read this book, although I'm not a materials engineer by any means.