Intel is showing 802.11ac based on the link rate of 234 Mbps (this link rate is not possible with N). Therefore, 802.11ac is working but not optimum since it's not communicating at maximum speed of 866 Mbps. This can be due to many reasons: poor drivers - most likely, interference from motherboard (least likely), poor internal antennas (possible). 5 GHz interference is unlikely since the Edimax can connect at much higher link rate.
My suggestion, flip the antennas on the 7260 connector and see if you get better speeds.