I have yet to start building my 1/2 but from what I have seen 8.5 to 1 is the magic number. I have seen and read about builds with 69mm cranks and 94mm jugs all the way to 82mm cranks with 92mm, they all start around 8.5 to 1 maybe 8 to 1.
Like I said though this will be my first 1/2 build and I have never tinkered with them so I have no real experience on the subject.