I extended the first two (three total) leg sections all the way and the last leg section about 1/3 of the way (base plate height at about 5' 6" or so), and hung my ~185 pounds from the tripod—no problem. The rubber feet squirmed around slightly on the smooth tile floor and other than that, uneventful. This is a seriously sturdy tripod. Fully extended to half a foot above my head, the last leg section will bow a little, so I didn’t want to push matter. Anyway, I don’t have a Zeiss 1600mm f/4 to worry about.
Joe Johnson of RRS stuff says “The 4 series tripods are SIGNIFICANTLY stiffer than the 3 (or 2 series) tripods and should perform better under any given condition — the draw-back being weight and cost”.
I observed no resonance in the legs, which can be a damaging issue with some carbon fiber tripods, e.g. with a slight breeze.
The TVC-44 is beautifully constructed item, with superb fit and finish—elegant. A tripod is a long term investment, so I make the investment and use mine for years. I just wish Really Right Stuff had offered their tripods earlier in my photographic journey, because my Gitzos developed various problems and with poor service turnaround too (they are mothballed now). The only thing I’ve had happen with RRS is some loose leg action (I sent mine in and it came back so smooth that at first I thought it was a new one, but it was mine indeed).
I ended up choosing the 4-section TVC-44 model because it extends to a height of 75 inches / 190 cm, which puts the base plate (without tripod head) about 5 inches above the top of my noggin. Not that I can see a camera viewfinder that high, but on steep slopes that extra reach is frequently useful. And more—see the Really Right Stuff discussion on tripod height.
In the field, I have used the TVC-24L and TVC-34L extensively (heavier/larger preferred, but that depends on hiking distance!). The TVC-44 now becomes my tripod of choice when I don’t have to carry it very far and when supporting heavier gear. Moreover, I generally prefer working with the larger models, in part because of the solidity and the wider leg-spread. Also, the knobs are easier to grasp and operate with bare hands or gloves.
See also articles on camera plates.