In your scenerio IMO the 4 lb of KE is not much of a difference. That said however there is another factor to consider and that is momentum (.511 vs. .638). The heavier arrow will have more momentum and therefore will penetrate more. Now is this factor enough to make you switch to the heavier arrow by losing 52 fps?
Then too you have the fact that these IBO speeds are a manufacturing standard of shooting a 350 gr arrow at 70 lb draw weight and 30" draw length. A shorter DL or heavier arrow will NOT give you this rated speed.