the internet speed showing in speedtest.net depends on the backgrond process running at the time of actual test.
For an example if windows is downloading updates.. another program tryin to download or upload somethin will affect the test results.

Try to run test in safe mode to get more accurate results.. make sure that other Computers or devices are not connected to your Network at the time of test.

and one above all advice.. dont bother abt the test results at all.. the differece is in mere KBs ...