Try to tone down the scratches in the diffuse and ramp them up with some contrast in the spec/gloss. I think you will be much happier with the results in the render.
PBR textures should have no lighting information (With the exception of Ambient Occlusion). This is unlike the old system where Ambient Occlusion would be put into the diffuse map.
why texture: for preview purposes, and I was going to experiment with Maya's Transfer Maps utility to create the diffuse map as well as normals. But it sounds like this is premature...