Those are recalibration (WOPC) points. It's the drie checking the quality of the disc & making adjustments on the fly (the X represents quality, and quality is what WOPC is helping with.)

It just happened because the drive recalibrated; you will notice, however, that the drive overall produced a better quality score with slightly less PIE and slightly more PIFs (but the PIF never go over two). This just seems to be a quality of the drives, both old and new.

Well, unless the are where the noticeable ring is makes the disc unreadable, and the disc quality doesn't degrade, then it is safe to say that a ring makes no difference. Other users have reported the quality is not affected; however, some do say that the quality takes a turn for the worst. And as for CS0T vs. CS0P...it's more of a personal preference. I prefer CS0T FBDX over CS0P.

EDIT: Also, notice the jump in PIE comes at the first recalibration point. This is the area where the drive would normally reach 8x; with the Fast Burn firmware, however, you notice it reaches 8x a lot sooner, and the drive has to set itself up so it doesn't use an improper laser power, among other things, for the remainder of the burn. (Imagine: the disc remains at 8x rotational speed--which slows down to stay at 8x--but the laser power is set to 16x, where the drive keeps a constant rotational speed--it is possible that the burn would fail or the disc would be unusuable; if the drive sets itself up to finish at normal 8x strategy settings, it will likely finish without errors.) It just happens that the 8x strat for the disc with this firmware produces a different PIE pattern. Notice: the maximum PIE for your CS0P firmware is much greater (and more mountainlike) than the max PIE for CS0T FBDX.