something is wrong because the non stop flight from sfo-pek on united is 5,914 miles each way, which means that's 11,828 miles. You can't have less than that unless you mean you aren't doing a round trip.

I'm sees some dates where united has it for $837

Also remember that once you reach premier, you get 4-500 miles upgrades for every 10,000 miles you fly on United. You don't get the upgrade for flying other carriers.