Best tripod for a pentax 645 600mm lens.

I have a couple of tripods, and one is a 4# Velbon lightweight carbon fiber tripod that i bought for a lightweight hiker mostly to use with my 4x5 folder for landscapes. It is rated at 25# and is adequate for short lens MF and 4x5 with a shortish draw, and it is pretty stiff, especially stiffer in the column area. It a lot stiffer than my bogen is for sure. I had a big Giottos and it was very heavy duty and stiff, rated for 26# but you could twist the neck and get movement. Not too great, but it could handle an 8x10 camera. IMO for a 600mm lens the Velbon is not going to be enough.

I already plan to get a Wimberly head for the monster, and am thinking about a berlebach. Anybody have another recommendation at around $300. I want something really solid I can use for 8x10 also.