The force of this site is that we are many people with different types of equipment for different jobs, sure RRS makes now some very fine tripods as well, the series 4 seems to be suitable for the job, only problem is they use too many leg sections, 4 and 5 - RRS is very much focused on how tall you are, and collapsed height for transport, not so much about what is the most stable for the lens in use,,, a bit wrong IMHO.
One of the major issues with large lenses is twist around the vertical axis, many designs do well in that regard,,,