5G is definitely more tolerable than 9G, especially in a GLOC situation, yet still allows for a pretty aggressive avoidance maneuver. The 5G limit is going to

5G is definitely more tolerable than 9G, especially in a GLOC situation, yet still allows for a pretty aggressive avoidance maneuver. The 5G limit is going to be decided in concert with the minimum altitude and an upper speed limit. GLOC would be most common at the merge, where they'll be at corner speed (the speed that allows them to get the tightest turning radius whilst bleeding the least amount of energy) and need to instantaneously load to 9Gs. So from an engineering perspective, I'm sure they massaged the G limit, minimum recovery altitude and maximum likely speed into the most optimal set of parameters, with 5G offering a good trade-off between minimum recovery altitude and pilot comfort. The planes themselves are G-rated to 9Gs, which is entirely a flight control system limit, because the bag of bones in the front seat tends not to do so well over 9Gs for sustained periods -- but the actual airframe will be able to sustain much higher before structural failures will start occurring.