macOS Sierra Download Time Est 33 hours
Servers are busy, try at another time of day, not when America is awake &amp; the EU are all home for dinner.

I got mine in about 40 mins, at around 8am, GMT

It has nothing to do with what DNS servers you use. Once you're connected, DNS is not even relevant. Your own ISP's DNS would normally be faster anyway, as it's [theoretically] optimised for your connection.

Rebooting your router/modem &amp; all network hardware, then your Mac may help a bit, fresh everything up.