At the moment, you have decent upgrade odds to F and almost guaranteed to C+ on flights up and down the coast and within the PNW. I wouldn't expect more than a middle C+ seat upgrade on a flight to a hub and even the non-hub TCONs are difficult. Delta sells F for cheap and Seattle, being an affluent area, people just buy it. Delta's new management does not want to give away F seats for free, so as time goes on, I would only expect upgrades to get tougher and tougher. Booking far in advance really doesn't help your cause as much as booking class, and even then you will still have dozens of GM, PM and DM ahead of you. I flew through ATL off-peak last week and there were 50+ people on the upgrade list. That being said, anything can happen and plenty of anecdotes as such, but I think the average of all anecdotes would indicate you need to keep your expectations low.