What this 40-position receptacle does in a board-to-board stack
The tin-plated posts (150.0 µ" / 3.81 µm) are solder-compatible for through-hole wave or hand soldering.
The key difference is circuit count: 40 positions on the 5-104078-2 versus 5 on the 1376775-2. The 1376775-2 carries a higher current rating of 3 A and a voltage rating of 250 VAC, but its gold plating is only 8.00 µ" (0.203 µm) — a thinner flash that limits mating cycle life compared to the 30.0 µ" on the 5-104078-2. For a high-density, high-cycle application, the 5-104078-2 is the better choice.