I have a bunch of primitive spheres I created in XSI and exported as .fbx files into Unity, but was wondering if I should scrap these and use Unity Primitive Sphere directly? Is there any performance gains using the Unity Primitive Spheres over ones created in a 3D application?
No difference whatsoever… the Unity Primitives were born from a very similar place 
Great, thanks! I will stick with the fbx approach then.
The shrouded ancestry of the Unity primitives has the historians in a fierce debate!