Fascinating to say the least! This is what I gather from reading the above posted replies:
String plugs seem to hold up better (with no guarantee) to the abrasion of either external particulate, or internal steel belted cords; but they may be prone to leaking air.
Between this site and two others, I have not received word yet of a "blow out." No horror stories yet of leaning her over in a 100 mph corner and blowing a plug.....
Plug-patches, readily available at auto parts stores, can be had that "vulcanize" to the rubber of the tire..... from the inside out, where it counts.
I plan to do another Track Day next month on some 014's sitting in my dining room. I will continue to ride AND INSPECT my plug/air pressure until such time as I take the tires off to be switched with the Bridgestones. When the rear tire is off, I will inspect the plug from the inside with the help of trained eyes, and consider vulcanizing the above spoken of plug from the inside out.