OK, that's a very good argument. I will vectorize it after finishing my GSoC application. 

Although... I'm still not quite sure the code is correct? I.e. I was happy to find vectors normal to the vertices in *forward['src'][hemisphere]['nn'][vert]* and I used them here... but does that really work, maybe I'm missing something that makes this incorrect, maybe there's a better way to find the normal component...?