Hey chaps,
I really can't confirm for sure but 16mm seems on the large side for a single 6 potter. 16mm is usual on road race bikes with a pair of calipers.
I currently run a 16mm Nissin master cylinder on my 4 pot Beringer and it is fierce. I think you'll find it was more like a 14mm master cylinder (or at least a 14mm might be better on the feel side of things), but I happily stand to be corrected.
Cheers,
Simon