Largest (safe) tablet size?

[YankeeClipper]

Naturally, having a sturdy mount is essential, and dimensions of the pilot can factor in. But for most of us in the "average" height and size range, how large of a tablet will safely sit on the center of the yoke without posing a danger (hitting your hands, flopping off/over, etc)? I myself would be looking a 51 year-old yoke, to be specific.