The upgrade to AC is actually huge compared to any N devices. Even comparing a behemoth-class N AP like the outdoor 7782 versus a Ruckus R500 sitting in a utility closet separated by a wall, the R500 is able to consistently deliver higher speeds to AC-capable clients.
Ruckus's BeamFlex technology does a great job of delivering a stronger signal to a bigger radius such that 802.11ac is no longer just a line-of-sight parlor trick, but rather clients at even substantial distances can take advantage of 802.11ac rates.
A lot of the advantage of 802.11ac actually comes from 80MHz channels, which only are practical to use in a low or medium density installation. In a super high density environment, there is likely too much co-channel interference to use 80MHz effectively.
