Low Wifi 5G speed with TP-Link Archer C6 v3

Installing and Using OpenWrt
21

As @slh mentioned, there is a difference between "theoretical" and "real-world" speed.

Run cat /etc/config/wireless

Redact the passwords in the "option key" sections.

Post the results in preformatted text, by using the icon highlighted in red...

OpenWRT Posting Icons

As you can see in this graphic, channel 36 at 160 MHz overlaps with 14 other channels -

22 
root@OpenWrt:~# cat /etc/config/wireless

config wifi-device 'radio0'
        option type 'mac80211'
        option path '1e140000.pcie/pci0000:00/0000:00:00.0/0000:01:00.0'
        option band '2g'
        option htmode 'HT20'
        option channel 'auto'
        option cell_density '0'

config wifi-iface 'default_radio0'
        option device 'radio0'
        option network 'lan'
        option mode 'ap'
        option ssid 'MIWIFI_2G'
        option encryption 'psk-mixed'
        option key 'xxxxx'

config wifi-device 'radio1'
        option type 'mac80211'
        option path '1e140000.pcie/pci0000:00/0000:00:01.0/0000:02:00.0'
        option band '5g'
        option cell_density '0'
        option htmode 'VHT80'
        option channel 'auto'
        option txpower '10'

config wifi-iface 'default_radio1'
        option device 'radio1'
        option network 'lan'
        option mode 'ap'
        option ssid 'MIWIFI_5G'
        option key 'xxxxxx'
        option encryption 'psk-mixed'