Yes BA CW is only better due to the flat bed but as I have said in another thread the WBC is pretty good IMHO.
A big concern of mine would be that you are taking a chance flying in December and not having all your flights on one PNR. Although a low probability due to your "positioning" out to AMS the day before, fog could delay you and where will that leave you?
Also you have to take into consideration the extra hassle of a longer journey and the cost to you in miles and fares for your positioning flights.