When I turn on the "power grid" overlay, there is a large frame rate drop which is proportionate to the amount of electrical things (wires, presumably) on the screen at the moment. So, zooming out allows more wires, which drops it the most. None of the other overlays do this, only power grid.
edit: Framerate seems to drop with all of the overlays, actually. It only runs at about 50 fps normally when zoomed out, but the wire overlay drops it to about 18. The overlays all hurt significantly, but not nearly as much (as the power grid overlay).
Lay a large number of wires, nothing ridiculous, similar to what you'd expect in a medium to large sized colony. Then zoom all the way out and try to pan the camera, and the reduced frame rate is significant. Do the same with any other overlay, such as gas or liquid, and it's fine, no decrease at all.