I've also been experiencing very sluggish browsing speeds and much slower than usual streaming speeds on youtube, netflix, amazon video, cnn, bloomberg, twitch (and fluctuating download speeds on a few gaming clients such as GoG and Battle.net) for the last 2 days. When I switch over to another account (WebAfrica or a 3G alternative), speeds are back to normal.
Speedtest.net takes a while to open, and when I am able to run tests (if the page doesn't time out while loading), it performs at about 10-45% capacity (1-4mb as opposed to the usual 9.5mb)
Looking at the line itself: there has been no packet loss when running tests, latency has been consistent and low, and I haven't experienced any line drops/desyncs. I've also played around with different DNS addresses, but it hasn't helped.