I've done a lot of speed tests over the last few months because of various problems on my fibre line. the thinkbroadband test consistently reports speeds that are within a couple of megs of the actual sync speed at any one time and I haven't found any other speed test that achieves this.
I suppose if you just stick with one test then you get to understand its quirks and its worthwhile anyway, but its nice to know that the reported download speed of a test is at least close to your sync speed. It also highlights that variations in the download speed are attributable to other factors.
Edited by ainsley001 (Thu 20-Nov-14 11:03:48)