So if the 7260n is valid, i suppose the 7260ac also is?
I am afraid I am not able to guarantee that as a fact, only the system manufacturer can.
So very strange only one wall can make this kind of speed difference, never had this problem with my other not AC speed adapter.
802.11ac works at 5 GHz which is more susceptible to objects and walls as it cannot penetrate as well as 2.4 GHz