It’s working as intended now. It takes ~800ms to generate the 1500 view on GT 705 this card is roughly the power of a switch but weaker!
Octahedron mapping to atlas
Cubemap UV view to atlas
Next is generating the Lightmap G buffer (LMGB) which mean I have to do a bit of level creation to have something distinct to also test if the unwrapping shader is correctly set.