1) afaik the 1700 series do not support MU-MIMO (3x3 MIMO with two spatial streams)
Multiuser MIMO (MU-MIMO) allows transmission of data to multiple 802.11ac Wave 2 capable clients simultaneously to improve client experience. Prior to MU-MIMO, 802.11n and 802.11ac Wave 1 access points could transmit data to only one client at a time, typically referred to as single-user MIMO.
the 1700 series is a 802.11ac wave-1 device -> you need the 1800/2800 series for mu-mimo functionality
2) 802.11ac only influences the connection between the client and the access point.
there may be other components between accesspoint and internet that may limit the internet speed