Will be flying YYZ-FRA on the 777-300ER. If I pay the advance charge to book into a "Preferred" seat on a Tango K fare, does that change the fare bucket of the flight such that eUpgrades would then be able to be used? (As a reference point, and not sure if it changes anything, this is actually a United K fare, but it's showing up in AC's system as Tango K).

Also, for more regular flyers on this plane/route, is it even worth the extra charge to go into a preferred seat? FWIW it's pricing out at $90/pax.