if you have two viewports it might take more resources.
depends on the complexity of the scene.
if you have vsync and multiple monitors, it might create issues.
ue has an optimization also, that when you’re not focusing on the window it will drop the fps on purpose (but it goes to like 15-30).
maybe by using 5 monitors and having the windows on separate monitors could introduce some overhead on the gpu. i don’t know but it’s an assumption. might be worth experimenting.