We've pulled a level X in almost half of the tins we've opened. Target had Lucario tins on sale for $10 each, and we pulled 2 Lucario X's in the packs, as well as a TSD out of 3 tins.
RE: have you ever gotten a level X (pack) from a tin?
Rayquaza C in a Rayquaza Tin IIRC. Shaymin and Flygon in a Darkrai Tin. Those are the only recent ones I remember. I've gotten many others however. Magmortar in Infernape Tin, etc.