SamKnows is single thread and three threads, and your result is similar to 3 times our single thread....
Our main test is 6 threads (we see Gig/Biz people pushing 600 Mbps+ over single thread) and speedtest.net is 8
As a rough guide if used the same sample dropping of ookla, an average of 58 Mbps would appear, and with no wobbly lines you'd probably not be panicking.
So given SamKnows and us are saying something is up, it looks like something is up.
http://tbb.st/1494663206761004755
http://tbb.st/1494664651243339255
And others on PlusNet are seeing decent tbbx1 vs httpx6 so nothing wrong at our end