Help!

[#1]

If the new values are shown correctly on your router's status page, then it should be using the new settings already.
So I wouldn't bother rebooting just for a DNS change.
Reboots are normally done when there is a connection issue, and DNS does not play any part in establishing your ADSL connection.
DNS is merely the mechanism that translates human readable web address names (e.g. "www.bbc.co.uk") to IP addresses (e.g. "212.58.224.138").

[#2]

And now my speed has dropped by about 1/3rd!!

INTERNET STATUS
ADSL Modulation : ADSL2 PLUS
Cable Status : ADSL Link Up
Virtual Circuit :
Connection Type : PPPoE/PPPoA
Network Status : Connected
Connection Up Time : 0:00:03:39
Downstream Line Rate : 4543 kbps
Upstream Line Rate : 444 kbps

MAC Address : 1c:bd:b9:8d:1b:4d
IP Address : 87.114.52.149
Subnet Mask : 255.255.255.255
Default Gateway : 195.166.128.238
Perferred DNS Server : 8.8.8.4
Alternate DNS Server : 208.67.220.220