Dear John,
Not sure which is the best choice for you.
I do not have much experience but I can tell you how I would do.
If I were you, I would check that the vest fits good for me and the gimbal does not drifts.
After that I would check to have no vibrations on the sled and to have a solid top stage.
If I am happy with that, then I would think first to have an arm I am happy with and only then I will go back to think about a new sled.
So for me the answer is (in order to archive the best shoot): the vest, then I would check the sled (gimbal, top stage, vibrations), then the arm and only at last a new sled.
Anyway wait for someone with more experience than me answer this question.
All the best,
Abramo :)