If you are flying QFE or QNH why do you want to know the elevation in metres? Runway thresholds are often a different height AMSL than ARP's as the world isn't flat, instrument approach plates show threshold elevation, but approaches are still flown QNH. One aerodrome I fly to has 20/02 with 20 threshold 21' higher than 02. Sitting on the threshold at Kemble looking in one direction is like looking up a ski slope.
Don't over think it. If your preference is QFE or QNH circuits/landings the VFR flight guides tell you the circuit height/altitude to fly, do whichever is right for you. personally I think the QFE and Regional QNH have had their day.
SND