Hi Neoprimitive, 

There is a fundemental limitation with Carrara from doing what you want – that is, Carrara only creates one type of sphere which is a quad-based sphere with triangles at the poles. By it's very design, the UV coordinates get pinched at the top as evidenced by GKDantas render. 

The way to prevent this is to create a sphere made of a polyhedron instead. In other programs, I've found the UV coords to map very well. In Carrara, a polyhedron UV will still need to be adjusted a bit to work well without distortion.

So, if you want to export an alternate sphere in Rhino for mapping in Carrara, it's a reasonable thing to do.

Mark