Hi Peter,
I haven't been following it too much and am not too good with the technical stuff but I'll give it a shot!!
From what I understand Cargolux and Atlas Air were both unhappy with the first few aircraft because they did not live up the specs promised. I think this was because they were heavier due to testing which made the first few frames less fuel efficient then they should be.
As for Cathay Pacific I think they are quite happy with the specs on the first 747-8F's. At the end of the day the first block aircraft are still much more efficient then the 747 classics and 747-400's they replace.