I've been using the AC68U as an access point with no problems with .205 firmware at all. I'm on FIOS in NYC and get insane speeds on this router. Even my neighbor two apartments down can get a great signal from it.
I just installed my ac68u as an Access Point, replacing an old Netgear WG102 (802.11g). My connection on 2.4GHz/802.11n is now 60 down/30 up. I even dropped the Tx power down to 50mw to reduce the signal levels out of the house.
I initially had an issue with MAC Filtering (weak security, just another layer to keep out the uninitiated) trashing the performance, but that was solved by upgrading to the 205 firmware.
All in all, a great upgrade in performance!