Higham rates better as an all round hooker at the moment than Clark IMO. His distribution and game awareness around the ruck is better, but obviously Clark wins hands down on speed and agility.
When Clark is the same age as Higham though, I dare say his career will have easily surpassed Micky's. For the 4 Nations I'd be picking Mcilorum with Daz Clark off the Bench. Nothing to be gained with an ageing Higham in the team for me.