I say 12 personally, good possibility it might be done at 11 though.
Ah okay that makes sense now, I was under the impression you were using just a MH not a CMH =P. Might have missed it in your post, but now it's been clarified....
You would be better off using the 250 HPS and using supplement lighting either from CFL's or T5's more lumens and still close to full spectrum in my opinion. If you don't want to go through the whole supplement lighting bit, then just use the full spectrum at least this way you still get the full spectrum. However your lumens will take a hit, and that chart shows the highest output color as blue and close to green which is neutral. Out of your 2 options the HPS with some supplement lighting would be the better and more balanced way to go. I think aside from the whole being in the better/right spectrum for better performance through certain stages of growth, lumens are more important than color.
Nice lavender toned buds by the by.