Just a side note but in your images- test 2 and test 4 the normals seem to be inverted. Flip the normals when you're baking or flip them in your rendering engine. Different software packages bake either direct X or open GL normals as a standard so its easy for this to happen.
I found the same issue: http://polycount.com/discussion/149028/padding-issue#latest There is no fix, it's a normal map limitation in Max/xNormal/Substance Painter. Maya just does this thing better. It might be because of the way it's applying the blur filter on the image, I had some better results with Mightybake, which…
I just knocked up a quick test to simulate your mesh. Exported from Max(.fbx) and baked in SP with default settings and no cage. This is using a synced tangent basis(which will be identical in UE4 automatically) EDIT: Sorry OP, I'm having a nightmare trying to embed my images. I see you've embedded from imgur. I've tried…
You're not the first, and certainly won't be the last to lose his mind over normal mapping!! :) Hard edges being split by UV shells is also the right way to go. It has been the method that's been used for a long time. Don't get disheartened. It is a complex subject with many variables. Just keep on doing test bakes until…