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I've been adjusting a little more, and I've actually found that I can get away with less infill, like you wrote, as long as the towers the balls are on (on the pelvis & chest) are all solid. About 5mm wall thickness does it.
Also, I've been experimenting with slicing each piece in half, printing both sides, then gluing them together with CA glue. My results are fantastic. Strong joints, almost no support material needed, and the outside looks great (aside from the seam). It's a pretty simple process in Blender, and I feel it adds a lot of strength. So far, I've done this on the chest, torso, and pelvis and I've had no breaks (Though I did bump the torso up to 102% because it was a little too small for a nice joint).
You might consider adding this to your current model, because it would make this print way more accessible (I could remix it, but I don't want to step on your toes).