Upgrades are covered
here.
Also, you'd see a riot here on the AS board if we were going over to SkyTeam/Delta and forced to do more SkyPiles intercontinental redemptions for our travel, and losing AA, BA, QF and CX. DL's availability at saver levels is MUCH worse than AA's (though DL J to Europe via AMS isn't so bad- we actually get it at 90K AS miles, less than DL's 100K SkyPile redemption rate).