If you're not planning on going into the Brize Zone, don't bother with a call to them. If Benson are there, call them for the MATZ transit but say goodbye ASAP (even before leaving the MATZ if possible) to call Oxford. If you are going through the ATZ you MUST call them, but even if you are overflying they have a lot of IFR training traffic around the OX NDB and it's a good idea for you to be part of their picture!