1Ks get CPUs before Plats, Golds, Silvers. In terms of CPUs, it DOES NOT matter if the Silver paid $500 more than you - a 1K will be upgraded first. The fare class difference DOES come into play when deciding which Premier within a Premier level gets upgraded i.e. a 1K on a H fare will be upgraded before a 1K on a L fare.

Capacity has shrunk with the merger and United is making headway at "rightsizing" planes to routes. Upgrades are becoming harder because of capacity reduction and fewer F seats (eg the switchover from 752s to 738s on the Hawaii routes ). The days of airlines losing money and making upgraders happy more of the time is over.