Weight-bearing is not the whole issue! The dampening properties (or lack thereof) of the tripod system are also important, because torque and vibration issues are additive. That's why I like both the mass and absorbing qualities of big wooden tripods for this kind of application. Thin metal tripods are the worst, especially if used with a type of metal head with a pinch point which further amplifies any vibration present, ball heads being the worst in an engineering sense. All this is just common sense. I do sometimes use a big carbon fiber tripod for this P67/300 combintation, but have it equipped with a center hook for hanging a bag of rocks if I need to give it supplementary weight in the wind or on spongy ground. I carefully tested all kinds of options. Even when I used a 4lb cast Bogen pan/tilt head atop myh big wooden Ries tripod and seemed to get good crisp shots, upon comparison with enlargements from my current way of doing it, with the camera bolted right to the tripod platform and no intervening head, the improvement in image precision is quite evident. Because anything you add above that platform is somehow going to act as its own torque vector in combination with the overhanging lens weight itself. This is basic. But some of you think you can make gold out of lead, or invent a time machine that defies the laws of physics. All kinds of things work, but some things work better than others. ... I might add, in response to J., that working with a long lens on a Hassie vs P67 might be analogous in certain respects, but when it comes to getting bounced around by potential vibrations, a Hassie is like riding a calf in a rodeo, while a Pentax 6x7 is like riding a bull !