Sir David's pension is calculated in exactly the same way as everybody else. His promotion is to do with maintaining service parity with his KCVO, that's all. He has done an enormous amount of good in the Royal Household - trimming down the huge amount of waste and culling the staff, whilst 'maintaining standards'. Not bad for an Adminer.
I think that we will see an increased rustication of Star posts from Main Building out to the Front Line Commands, with a concomitant movement of the supporting staff as Centre costs are driven ever further downwards. Gone, sadly, are the days of a pied de terre Pimlico, Putney or Docklands. Try a shared bed-sit in Croydon for the lucky few posted into Defence HQ.