Have given up on the BTw performance tester since the "new look" interface appeared a few months ago.
UL consistantly reports speed 4 to 5 Kbps greater than my UL synch speed !
DL speed is consistantly reported1 to 1.5 Mbps greater than any other speed test utility.
Occasionaly still use to check DS BRAS IP profile disregarding the speeds reported but more inclined to use mouselike.org now.
Have found that the revised utility is less sensitive to browser being used, the previous revision definately did have issues with Firefox on a Win 10 platform.