rdgrimes, I agree that faxmaster's graph is indicative of "summer-time slowdown". I have two LTR52246S drives and both were capable of burning TY at 52x with low error rates under normal weather conditions (not too hot).
That is, until we encountered some days over 100° F, when the temperature in the house approached 80° or slightly more. Although my computer cases are well ventilated, the higher temperatures showed up in higher error rates and some C2 coasters with TY discs when burned at 52x. This was happening to one burner in particular, and the other seemed relatively unaffected. This was the first time that TY had delivered C2 coasters, and I thought perhaps the burner was failing until I realized it was just the heat. The stress of burning at 52x, immediately doing an error check at the highest speed, and then successively repeating the process took its toll.
After I figured out the problem, the next day I retested the discs that had shown C2 errors (when hot) and most C2s had disappeared. As you mentioned, the pthalocyanine discs (Maxell 40x) were more resistant to heat, and still burned OK at 52x with low error rates. As the weather cooled a bit, the TY problem disappeared.
One of the coasters did reveal the unreadable sector issue. If this is caused by the invoking of SmartBurn with 52246S drives, it is too little, too late, and defeats the purpose of SmartBurn. It isn't so "smart" if it causes an unreadable sector instead of preventing it.