The following is from united.com. It seems that premier with B fare has priority than W fare with GPU for long haul flight. Am I right?
The following is the order of priority, within five days, on flights that are eligible for Complimentary Premier Upgrades:
Premier members on eligible Y- and B-class fares, as well as Premier 1K members on M-class fares: Instant upgrades that weren't confirmed in advance, sorted by fare class, then Premier status
All travelers on waitlisted Global Premier Upgrades, Regional Premier Upgrades, and MileagePlus Upgrade Awards: Sorted by Premier status of the redeeming account, then fare class and time of request
The following is the order of priority, within five days, on flights that are eligible for Complimentary Premier Upgrades:
Premier members on eligible Y- and B-class fares, as well as Premier 1K members on M-class fares: Instant upgrades that weren't confirmed in advance, sorted by fare class, then Premier status
All travelers on waitlisted Global Premier Upgrades, Regional Premier Upgrades, and MileagePlus Upgrade Awards: Sorted by Premier status of the redeeming account, then fare class and time of request