Originally posted by Sandy Hancock Sigh.
The further you have to separate your hands to balance a front heavy lens, the less stable the hold.
Hmmm... I would have said the opposite. With my right hand on the grip and the camera against my face, the camera end of the system is pretty stable. The left hand supports the center of gravity and does the little micro-motions to refine the pointing of the camera. In this configuration, the further the left hand is out under the barrel, the less a given millimeter of hand motion turns into some number of degrees of angular motion.
Note that the manual for my first camera (am OM-1) taught me to hold both elbows of my arms tucked against my torso when I shoot. For long heavy lenses, my left elbow tends to move forward to brace against my ribs, making it even more stable. I'd only run into trouble if the CG of the lens-and-camera was more than 300-350 mm from the back of the camera. That covers almost all the lenses in the Pentax arsenal with the exception of the 560/5.6 which looks like it might have a CG around 400 mm from the back of the camera and probably isn't very hand-holdable even with a grip.