With SFO being a UA hub with lots of elite flyers, it will be a challenge to get upgrades with them, and, if you do fly 100K the international upgrades require a higher priced fare snd no fare credit if you don't clear. Having said that, it's hard to beat their schedule and there will be trade offs if you fly someone else, particularly in terms of numbers of flights.

Alaska, particularly for SFO and SEA based flyers, may be a good fit for for most of your destinations. Let me go into more detail when I have more time later. They do offer free SDC and refunds to top tier elites. Possibly they may extend that to midtier 40K - need to check that

Tom in Fremantle, Western Australia today