Serious question mate - how many seasons do you thinks Jags has left making 40+ starts at Prem level? I reckon that (barring any serious injury) he's got two seasons at his current standard, one at a slight drop off and then one where he will show substantial decline.
Galloway and Browning are not the right partners for Stones quite yet - both could do with going out on loan and getting regular starts in order to push their development. Sitting on the bench for us and getting ten minutes once every five or six games for the next two years is not the way to maximise their development.
So I think we should be looking for someone around the 23 to 26 years old range, who could come in and make 20 starts a season if injury to Stones or Jags necessitated it. And wouldn't it be a good idea for that incoming player to be approaching the standard good enough to ease Jags out of the starting lineup in the next two to three years? I don't see the point in waiting until it becomes urgent.
For the next couple of seasons at least it will John Stones not Phil Jagielka who will need taking out of the team for a rest.
Jagielka is a battle hardened experienced professional who can play week after week.
John Stones, is a tall gangly young man who will be under severe scrutiny in every game he plays for all sorts of reasons, he is the player that may occasionally need to be given a rest to refresh his batteries.