Further brief research suggests it's "flight time with one failed engine" that's a constraint, somewhere between 60 and 180 minutes, depending on how the plane is certified. The Gulfstream 5 is a twin-engine aircraft, which makes it more awkward for crossing large bodies of water. For long-distance flights, you're more likely to be on a four-engine plane, which has more lenient safety margins in case of engine failure.

That said, the Pacific has a good chunk of diversion airports available as well.