I just look and figure if I can make it or not. That can take a lot of things into account, such as how alert the critter is, lighting, etc. But I don't think about it too much. Just decide and shoot or not. That being said, I do a lot of practice standing on a step ladder and I always take a judo shot or two before leaving the stand, so I actually shoot better from a stand than on the ground, it seems. Weird.
I have never taken a shot past 9 of my paces, so about 18 or 20 yards, but I've passed several a lot closer than that for whatever reason.