What else can affect your speeds on WiFi? Cordless keyboards, mice, baby monitors, RC Toys, garage door openers, cordless phones, Microwave ovens, Bluetooth devices, (like your wireless game controllers), ALL of the wireless networks in your area, and physical obstructions such as walls, doors and even furniture can cause WiFi interference. Then you have EMI interference, monitors, TV's do you use fluorescent screw in light bulbs? The obstructions, if you have Device electronics in between like TV's/stereos. or hardened walls like bathroom walls, or a laundry rooms.
I once worked with someone that had a smart house, and the router was INSIDE the wall in their downstairs laundry room. Think all that wiring surrounding a wireless transmitter, that's like putting it inside a faraday cage! Then it has to go through walls, steel door to the box, and the washer/dryer to get to some of the places in the house.
The ONLY accurate speed measurement will be a wired ethernet computer, using at least a 1000baseTX connections, ot a 2.5gb connections.