Originally Posted by Cathay Boy

A higher class fare does NOT increase your chance of op-up, op-up is primarily based on FF status. So unless you plan to use mileage upgrade there's really ZERO reason for you to want to spend that extra money to get the K instead of just flying M.

Also, different classes do have differences in small details, but they are mostly logistic differences like how much to pay (or not pay) when you change time, change date, for how long, etc. Not a difference in mileage earned (not CX anyway.)

Yes, different airlines have different rules so study up.