Loosen up your edges a little bit. Also I think your low poly has all hard edges. There should only be hard edges on UV island borders. Also are you using a cage for baking?
As described in those threads, one of the way to gat rid that - to do UV seams alond the edges, but result was not satisfactory too. So i added the supported loops along hard edges
You need to have uv splits everywhere you have hard edges, otherwise you will get errors. You also need to bake with a cage, otherwise everywhere you have hard edges, you will get gaps in the projection.
after that add to the upper layer the white mask, and add the generator with MG Metal Edge Wear. Invert that and got nice result with plenty scratches on the curves and hard edges, and some scratches on a flat (just some corrected the settings of MG Metal Edge Wear). so its just two materials with generator of scratches in…
Or, may be, i have mistake with using smoothing groups, almoust all problem places are on the hard edges, places of contact polygons with different smoothing groups.
You have to make seams on any edges that are required in order to maintain undeformed topology. lack of seem inside the rounded hole will produce errors and stretched texture.