I'm actually looking for Xmax generated distortion, not Xlim - so I think harmonic content is going to be a more reliable indicator, but I'll give that a try (once I get my inputs working again).
I have a commercial box which is disappointing me, farting out even with a sub handling < 100 Hz. I'm trying to figure out "the excursion limit is 95dbA @ 120 Hz" or whatever.