What to look for is simple: steady for the weight it has to support. If you spend 3K on optics and the tripod is flimsy you just downgraded your optics to 500 bucks -- the vibrations the tripod transmits do that. To give you an idea, for a 85mm spotter I'd go for something like a sirui 3213X (I use it for a 80mm spotter), and not even bother to use the center column if you can avoid it. I do understand that in practice what I am saying sounds like 'forget lightweight and compact, get something big, heavy and difficult to pack', which is not what people want to hear, but the 3K -> 500 bucks decrease in optics performance is no joke. A tripod with a 3 sections leg will always be better for a 85mm spotter than a more compact 4 sections leg. A heavier tripod will also do better. The only place where I could see a way of making stuff lighter is to get a ball head (because they are really strong for the weight they can take), which can be 1/2 the weight of a fluid head. You will immediately get in the tradeoff lighter-easier to carry/less stable - more vibrations. In theory you can hang stuff from the bottom of a tripod and increase the stability, but then again, that works best if you can hang a lot of weight (which you might need to find on location, unless you like to pack it especially) and hang it so it increases stability without adding oscillations -- doing it well requires finesse. If you know how to do that well, you know you will find decent weight on location etc, you might go for a lighter rig. I personally would not unless I had *years* of experience in weighting down a tripod -- it does not take a lot to run a hunt.
If you know you will do all your spotting *sitting down* then you can go for something smaller, because you will just use the first segment of the legs (give or take), which is the sturdiest. I would never make that assumption for myself.
I understand none of the above is stuff people like to hear. I apologise.
