Since joining PlusNet my internet connection speed has been consistently slow with periods with no connection. Going back 2 suppliers, BT, I had the same problem, so I left them for TalkTalk. For several years TalkTalk service was good, much faster than BT with no congestion problems at peak times as with BT. I left TalkTalk because their service failed consistently for long periods between 07:00 and 08:00 every day. So I am now back on BT kit with their old overload problems.
I run RouterSats which gives a line down connection speed of 3648kbps. This is rock solid.
I also ping my own domain every second and log the delay where the round trip is +- 10% of the average. This often times out.