...I just use miles for C when the price of the ticket in C in miles is similar to the price of the ticket in Y in cash. Free upgrade for minimal additional cost. I havz done more elaborate quadratic equations, but not worth the effort any more.
^ Exactly!
No reason to ride in Y on a 16-hour* flight when it costs about the same to ride in J.
*and in J, I always root for strong headwinds.
