I don't think wifi is the problem. I had the Archer A7 connected to the main router through 5GHz as a client. I also setup the 2.4GHz N as AP. With a laptop connected to the AP wirelessly, Ookla speedtest gave me something like 70Mbit.
Yes, low power consumption is a big consideration to me. I started with Asterisk on a mini desktop (230w PS), move to a thin client (60w PS) and finally to Pogoplug Mobile (12w PS). My OpenVPN server originally ran on a Netgear R6400 (DD-WRT) before moved to the Pogoplug alongside Asterisk. I get something like 16Mbit (max.) out of Ookla speedtest via OpenVPN connection, So I am quite satisfied with the Pogoplug Mobile handling both Asterisk and OpenVPN. It is just this desire to consolidate further (one device for all three tasks) biting me once in a while. 