Attached a shot showing the loaner lens performance summarized. As you can see it's very sharp in center, and at 100mm image circle it's sharper on one side than the other, clearly seen at f/11. However at f/16 the difference is not too large. The loaner lens is performing better than my copy.
I also dug out a SK60XL test with the IQ180 probably made by a dealer (Doug perhaps), and it shows the same, that is at f/11 one side is considerably sharper than the other at 100mm image circle. So all three SK60XL lenses I've pixel-peeped all show a clear left-to-right difference at f/11, which leaves me with the conclusion that it should be expected with this lens, but that at f/16 the good copies should not differ much.
TJV's Rodenstock 55 shots earlier in this thread they show crops at about 80-85mm image circle at f/16. I don't show that in my attached screenshot so you have to trust me on this: the SK60XL on its good side makes a much sharper at f/11, but on the bad side it's about the same as the Rodenstock at f/16. Stopping down the SK60XL to f/16 the differences evens out almost completely, but the result is only marginally better than the Rodenstock 55. Possibly if we go out to 100mm the SK60XL would win.
If it's possible to get an SK60XL copy that really is as sharp on both sides as this one is on its good, then you could shoot your panoramas at f/11 and clearly outperform the Rodenstock 55. However seeing three SK60XL copies and all three having pretty strong left-right differences at f/11 it seems unlikely to get a copy that performs at that level.
I suspect that my lens that is about to come back from Schneider-Kreuznach without action will show that it performs as bad as it did when I sent it in. They did not find any error and even said that it performed better than their spec. If this is true it means that if you have a bad copy it won't be possible to get it aligned either as the repair shop don't aspire to that level of quality. So far that's speculation though, but it doesn't look too good.
ALPA is said to have custom calibration of their lenses. Anyone who knows who does that, and if it has any effect, or if it's just market speak? If it's Schneider-Kreuznach repair shop that does it, it doesn't look promising... I would certainly be prepared to pay for a remounting service if you could get the lens to perform at the same high level both on the left and right side. One of original reasons for using medium format is to get better precision in lenses, but the observations I have on this lens so far makes me doubt that there really is any truth in that.
I'm not sure the image is displayed correctly here in this forum, so here's a temporary link to the image
http://torger.dyndns.org/sk60xl-loaner-analysis.jpg