You're getting a little confused, (not surprisingly), by what's involved.
Taking the simple one first, the whole point of the interstitial faceplate the engineer fits to the master is that no re-wiring at the master or to the existing faceplate is required. All they change are the screws holding the faceplate on, using longer ones to go through both the faceplate and filter plate. See this page
The result is that all the extensions have the broadband filtered out and are phone only. Which is why you would need to remove it. And find the shorter screws then needed!
Now to the speed. Do you know your estimates from the BT Wholesale Checker
Unless you have completely screwed up wiring then using the extension should make little difference. That's a different discussion. BT Retail, Sky and TalkTalk no longer send an engineer and just supply their modem/router and a dangly filter, just as for ADSLx.
Having the master moved, unless once again your wiring is completely screwed and the engineer realises it and corrects it, again makes absolutely no difference. The same amount of the same cable is still added to your distance from the cabinet, so the speed loss is the same.
Edit - And if the wiring is currently screwed then even an installation at the master needs a pukka OR engineer to realise and correct it.
Edited by RobertoS (Mon 20-Apr-15 16:10:04)