It sounds like your carbon fiber tripod would probably do the job. They are strong and stable, and they seem to resist shock pretty well. The Pentax 645 doesn't have a real bad mirror slap or shutter release shock. You might try to set up a test comparing results on that tripod between the 600mm and a shorter lens for roughly similar image sizes. What you choose for 8X10 may be overkill for 645. If you do have to go for something bigger than you have, both carbon and wood are attractive. The wood Berlebach are very nice and quite sturdy, but they have some real disadvantages, too. They have limited extensions, and you have to extend the upper sections of the legs before the lower sections, because of the way the clamps work.