Speed tests over WiFi are inaccurate. The only accurate way of measuring provided throughput is going to be with an Ethernet connection using either 1000baseTX, or higher.
Wireless is affected by many factors, Cordless Phones, microwave ovens, bluetooth devices, cordless keyboards and mice, (They can use 2.4 OR 5 ghz), Game controllers, baby monitors, garage door openers, , radio controlled toys, as well as every neiughbor with a wireless router as well as the above mentioned equipment.
There are things you can do to improve your connectivity and speeds over WiFi, Ensuring you are using a band that is more open than the others, ensuring the Wireless router is out in the open, not behind or under anything. Trying to make sure there is the fewest number of solid objects in between the wireless router and the device using WiFi.
Also remember, 5ghz, has ½ the range than 2.4 has, so while it's faster, at 25-30 feet, you are best served by being on 2.4.