I'm going to hate myself for posting this, but oh well...
Back in 2009, I had 5 different speaker cables I was trying. All of them basically copper, and I don't think any of them were OCC. All had similar geometry. 3 sounded similar, 1 sounded very bright, and 1 was a mistake from a test batch of cable that sounded so dull it was like I put tape over my ribbon tweeters. Out of curiosity, I set up my measuring gear, and proceed to measure each cable. I ran the measurements twice, only changing the 1 speaker cable. The test took maybe 10 minutes max both times. Even though the 2 cables on the extremes sounded VERY different, every measurement was nearly identical. What I mean is when I had all 5 measurements displayed, I could only see 1 line. This happened exactly the same for both tests. So what was at play here? How is that possible?
Since that test, I put much less weight on frequency response measurements. They just don't tell you nearly as much as people think they do. It's just a small part of the story. Where is the measurement for clarity?
No offense to Dave, but I too think measurements done days apart cannot be trusted. There are far too many variables at play. That said, what he found might still be possible, but I'm not certain how audible the change would be.