I've done speed tests dozens of times. A few things I've noticed:
1. Though I have significantly higher speeds, pages made "load" quicker but, I'll still see an activity indicator. The pages don't load asynchronously in other words.
2. Speeds seem to spike up and down quite often.
What gives? They double my speed at no cost to me, but I don't see much improvement, but speed tests indicate that I should be seeing improvement.
https://rescomp.stanford.edu/~cheshire/rants/Latency.html
Discussed at length here on HN:
https://news.ycombinator.com/item?id=7826768
Many other articles on roughly the same topic:
https://www.google.co.uk/search?q=It%27s+the+latency+stupid