212 - see HEDPs post. At cloudbreak on mimimas using QFE you know that a 150' DH on PAR means the runway centreline is 150' beneath you - with a QNH approach you have to subtract the elevation from the DH to know how much space below the cloud you have. It also means that METARS (based on airfield elevation) are directly relevant to your DH/MDH when looking for diversions.
Nick - I can't see how writing 3 pieces of information on a kneeboard is easier than adjusting one knob on an altimeter - I'm sure the Human Factors guys would have a field day with that one
Cyclically - don't bother asking for a MSD clearance, it doesn't exist. My question for you is - when outside the MATZ and operating on QNH are you using a rad alt to determine your height agl? If you are using altitude on QNH compared to ground elevations on the map then you are still very likely to go below 500' agl unless you add a healthy margin. My answer to your original question is still - look at the map and ask for a suitable clearance through the MATZ based on QFE that will keep you above your 500' agl. Alternatively give the unit a ring before you launch and tell them what you want to do to see if they can suggest a suitable clearance height.