It'd say around 2px on each side is super safe if you're rendering at roughly the same resolution as your source texture. If you're scaling it down, you're more likely to get artifacts around the edges.
Rule of thumb for super clean edges: Padding should be bigger if you're using meshes. Padding has to be bigger if the resolution is higher and you intend to scale down at runtime. And it has to be bigger, the smaller you intend to scale it.
I'm talking about padding when you export your image parts for use in Spine. Not padding when you pack your atlas. Region padding only needs to be 1px. At most 2px in any case.
I don't think this information applies to you if you had 50-80px padding already. But note I'm talking about padding within the meshes, not just padding on your source textures. It's just that you need a minimum amount of padding on your source textures so your mesh can have some space to work with.
If you had 50-80px of padding but you specifically created meshes that chopped off or extremely bent at opaque parts of the image. Then really, that's what's causing the artifacts (sans MSAA).
The rig isn't too informative. The mesh (where it shows the vertices and sides and triangles) will show you why you're getting artifacts.
The point is to move the outer vertices and sides of the mesh away from the opaque pixels of the images.
