The Qualcomm Atheros QCA9880 802.11nac in my Archer C7 v2 running OpenWRT 15.05 only seems to perform when really close to the AP. Btw I recommend OpenWRT over the stock TP-LINK firmware!! I found it faster for a start.
My first test was from behind my study door, about 5m from the AP… ~15MB/sec
Second test from my study table where it was barely usable, aka out of range. I’d say just over 10m away through a door.
The last test was almost 60MB/sec where my computer was right next to the AP.
Update: Opensource Wireless AC doesn’t seem to exist sadly. :(