9w1: "I must do this perfectly." Having a perfect picture in their mind on how things should be, 9w1s may have difficulty going into reality to bring this to fruition: it's enough to imagine, otherwise the picture might come out wrong. Have the ability to change their surroundings for the better when healthy.
9w8: "I must live up to their expectations." 9w8 will feel the need to do what needs to be done, but not up to the task. This results in the classic Nine-ish shut-down: it's too big too handle, I will never be able to do it. When healthy, their mere presence gives off comfort and they finally have the confidence to tackle life.
The subtlety between the two wings interests me

It seems, to me, like both react to stress the same way (essentially ignoring the cause), but the reasons are different.