Does better bodies cause any noticable FPS hit?

Not usually for most people but I've noticed in places with lots of NPCs it can cause a slowdown.

Maybe if everyone's nekkid? Otherwise the mesh itself rarely shows except for forearms to hands and ankles to feet.

Counter Intuitively, Better Heads and Better Bodies have less of a load on the system. While their polygons are smoother, there are usually less of them, so the system does not have to process as much data.

I know that I saw a slight FPS Rate increase on my rig back in the day when Morrowind was chewing up PCs and spitting them out if you dared show up with less than stellar pc parts.