The best person ask would be Jerry Powers. He did the development work for the McDermmit cues. I think they were called the I shaft series. For some reason I have him in my mind as being associated with the G core shafts as well.
Neil
I called McDermott and they told me I could take it down to 11.75 but absolutely no more than that ;-) I still didn't take it down far - just didn't feel right.
Thanks!