Quote from mark1:
What prolly happened were periods of very high ping response, or dropped packets.
My personal experience bears this out. Was having serious delays in data, worked with my Brokers Tech Support and traced the problem to high packet loss - up to 20%.
It was explained to me that the servers are set up to ensure data integrity, so until packets that have been sent are confirmed as received completely / correctly, new data is held back.
Sorted out the problem with my ISP and the data delay issue was resolved.
Since then I am much less concerned about raw speed and pay more attention to the ping test.