Is the connected device also 3x3 Wireless-AC?
setup is virgin media modem mode>6x6 dual core ac3200>3x3 single core ac66u>wired to pc.
speed test posted was taken by wiring a laptop into the ac3200. according to the asus dash the ac66u unit syncs over the 5ghz channel at approx 1gbps.
I have line of sight over a distance of 8 feet.