Do you have any issue with lost packets?

Even packet loss of a few percent can slow TCP transfers down a lot.

Try 100 or even 1000 pings to the BBC or a Google server.

Just to confirm that I am having a near identical experience as rinbad... Predicted speeds were 58/18 and reality is 40-45/8 .

However Zen support say that the Openreach modem is syncing at 60/20.

Taking all cabling/routers out of the equation with laptop directly plugged into modem its still 40-45/8.

Did you get a resolution at all?

Thanks

Mark