MTU

[#1]

I am on the trial with the netgear router is the MTU still the same as normal adsl2 ie 1492 or does it need to be changed for best speed etc. This is on the router what about on the pc?
The other thing is should the modem every die can you then connected back with a adls2 router the thompson as a temp fix or wont it work?

[#2]

The MTU does not need to change.
Once on FTTC you no longer have an ADSL connection so you can't revert to using an ADSL modem/router without BT uninstalling the FTTC connection in the green cabinet.
FTTC uses VDSL and PPPoE which is not compatible with ADSL and PPPoA.

[#3]

Out of interest, see here http://wiki.aaisp.org.uk/index.php/FTTC_Modem , there is a slight tweak possible according to AAISP if your router is capable of it.
I have no idea if the Netgear router supplied supports those standards mentioned in that wiki.