Wizofoz,
9.G is absolutely spot on with everything he says.
Cat 3a does not require 125m mid (as the ground based system assures rollout). Only if your aircraft has a degradation do you need to apply 125m instead of 75m.
I also fly the B777 for a EU-OPS compliant carrier and I think you need check again your airports. There are plenty of Cat3a only runways both in Europe and outside. Try Hannover 27R for starters. So when mid drops to <125m you divert while we land ? Commercially your company should look at this again,