Pacific Gem was released in 1987, one of New Zealand's earlier high-alpha bittering hops and a variety that built a specific, lasting reputation around its unusual black currant and oak character — a combination distinctive enough that it's remained in steady commercial use for decades even as newer, more tropical-fruit-forward New Zealand releases have captured more international attention.
At 13-16% alpha acid, Pacific Gem functions primarily as a bittering hop, and its dark fruit and oak notes have made it a traditional choice specifically for stouts and porters, where that black-currant-adjacent character complements roasted malt in a way most citrus- or tropical-fruit-forward hops don't. This gives it a genuinely different role than most of the higher-alpha hops on this site, which lean toward pale, hop-forward styles rather than dark beer. Pacific Gem's high, dependable alpha range has been built up over decades of commercial use, which the IBU calculator will translate into a real figure for a Pacific Gem-based charge.
Bravo is the closer American substitute given its own black cherry note, sharing some of Pacific Gem's dark-fruit-adjacent character at a similar alpha range. Columbus offers an alternative for pure bittering efficiency without the specific dark fruit note. Stout, porter, and darker New Zealand ale styles use Pacific Gem where that oak-and-currant character is specifically wanted. Pacific Gem's alpha floor matches Columbus's almost exactly, while Bravo's range sits a step higher, why Columbus is generally the closer substitute for matching bitterness at the same weight.