Anyway, the change is booked for 11th April so it will be interesting to see what happens.
Please do post back to let us know. I too have had this issue with Zen for past 12 months and gave up trying to get them to fix and have all but accepted nothing single threaded gets full benefit of the connection. For various reasons I'm going to have a second line installed soon and I'm going to try Talk Talk Business on that and directly compare against Zen.
As requested I am reporting back on the changes that IDNet made to my connection. I don't know exactly what they did other than that it involved a "reconfiguration" which took place just after midnight on 11th April, so obviously not requiring the services of a BTOR engineer.
The net result is that I no longer see any packet loss and my single thread speed is back where it should be. The only other difference is that my minimum latency has doubled from 10ms to 20ms, but I am not a gamer so that isn't an issue for me.
I call that a pretty good result and my thanks to Brian at IDNet for seeing it through.