I have found that CX is pretty generous when compared to SQ. Not quite as many seats as BA but pretty good!

The best way to check is to go to ITN in the advance mode and look at seat availability. Look for 'A' class numbers which is for First RTW. You find probably find that on certain times on certain CX routes they have fewer number of 'A' class seats. For example, CX has (I think) two flights a day from HKG-LAX. One of them normally has more seats than the other. Also depends on the day of the week. Hope this helps!