OK guys here is an tricky one ( for me anyway )
Just changed to Fibre and a comparison with a mate showed he was getting faster downloads on copper than i was getting - Hmm.
Got onto ISP and techy came out and after a lot of trying things, have the cause, i think but not sure what to change/check/fix.

Here is what we ended up with: Time Caps connects to their server PPPoE and with 3 computers connected to Time Caps by ethernet leads - the PC laptop with windows gets 30/10 speeds, the iMac 20 on 10.6.3 gets sloooow downloads using speedtest.net in Safari to local server and the iMac 27 on 10.8.3 gets sloooow downloads using speedtest.net in Safari to local server BUT THEN if i use FireFox, in either iMac, doing exactly same tests speeds are same as PC. Both iMacs were open in a new admin user.

Any ideas out there?