BTW the connection speed may also depend on other wifi APs / network activity in your neighbourhood.
Check used channels in your area.
Don't forget that only 1, 6 and 11 are really independent, all others skirt into the neighbouring channels, i.e. if your neighbour has his AP on channel 4, you should be on 9 or higher.

BTW WiFi as a system deals better with collisions on the same channel (slot time sharing required) than on adjacent channels (noise/disturbance, bad reception at all times). That's why Bluetooth is a major disturbance to Wifi, quick channel hopping, so mostly a signal-to-noise degradation for the Wifi link.
So if your neighbours are on 1, 6 and 11, best go on 1, 6, and 11 too, unless their link signal is weak, so your signal can just drown it, then go on an adjacent channel - your stronger signal / link should not be impacted much.

Disclaimer: this that and the other from putting bits and pieces together - I'm not an RF engineer.