IMHO, it just isn't worth the spend of miles to upgrade from J to F. The food is basically the same and the wine as well. The seat is a bit better, particularly for sleeping, but the AF J seat (on 772 and 773 at least) is quite nice. Really, the lounge difference is negligible and service is just basically the same. I'd save the miles for something else. AF F is nothing to get all excited about.