I doubt it would be more economical. I strongly suspect someone did the analysis, determined that at five 9s they earn $X, at six 9s they earn $Y, and the diffe

I doubt it would be more economical. I strongly suspect someone did the analysis, determined that at five 9s they earn $X, at six 9s they earn $Y, and the difference between the two is large enough to be worth funding the projects to get there.