My flights to and from ORD in the last week were chokka in both directions despite my predictions for quiet flights. Four days out when I consulted Expert Flyer, it showed plenty of free seats in all cabins so my wild guess is that BA may be getting the lion share of last minute bookings on this route. If this is by any means a representative example, it would be worth enquiring about paid upgrades at check-in.

I suppose its quite feasible that you are op-uped to Club and your partner stays put in Y