Richard,
Have a look at the test w/Campbell (GD, May). He was over 30 yards longer with the new club/modern ball than with the old club/modern ball, more like 10%.
Jim, I just read up on the article and there are a couple of things you need to be aware of.
1. The main difference in distance is coming from the swing speed. Chad logged 113 mph with a modern driver and 106 with persimmon with a 43 inch steel shaft. The article indicates that this alone would account for about 15 yards (~5%), which I agree. Which is perfectly consistent with what I had said before. In fact, if you switch that steel shaft with a 44 or 45 inch graphite shaft, you will see even less difference in the swing speed (which does not have anything to do with the persimmon head).
2. If you look at the chart, you will see that the smash factor (the conversion of swing speed to ball speed) is identical between the modern titanium and persimmon driver. However, with Chad's swing, the persimmon driver is producing too much spin, which is what accounts for rest of the distance difference. I would argue that if you took time to custom fit a persimmon driver head with lower loft that produce less spin, you can get back that additional 5% difference that the article noted, which would bring us back to 5% difference.
The identical smash factor CLEARLY indicates that when hit in the sweet spot, there is really no difference between a modern titanium driver and the persimmon driver. The only difference between those drivers are coming from the shaft length and weight (and not COR).
When Adam Scott went through the test, the results were very similar. He had identical smash factor between titanium and persimmon drivers as well. But the persimmon driver fit Adam much better and he was able to produce better trajectory (with less difference in distance as result). He even commented that he could have gotten a few more yards out of the persimmon driver if he had a couple of weeks to practice with it.
I just don't see any evidence that COR or even the titanium head is that much of a difference in distance as you believe, at least with these pros as they hit the same sweetspot on almost every swing. The bigger differences are coming from the shaft and the ball.