I'm still new to blender, and I have found a problem that I can't solve.

I'm importing some models to blender from a certain source, but when I use "Rendered" viewport and try to apply some lighting, sometimes I get inconsistencies with shadows/lights on some faces.

Here is an example with an arm (but the problem can also happen in other parts/models in major or lesser degrees): Rendered

As you can see there are abrupt changes with light and shadows between faces, but when I'm working with "Material" viewport all seems to be ok:Material

I have tried many things to smooth the mesh like: smooth vertex, faces or edges, clear custom split normals data, recalculate normals, remove doubles, auto smooth, subdivision surface, edge split and others things like different lighting configurations, but nothing really helps. The only thing that helps is applying subdivide smooth two or three times but it creates too many faces and that's probably a bad thing.

What could I do to fix this problem? So I'm able to use those models and apply light to them.

I'm using Blender 2.79 with Cycles Render

Here is the .blend file, I uploaded to Mega because Blend-Exchange was not working for me right now https://mega.nz/#!uQUH2KSK!aOkH8S33vvv1NYqmYMaigNWsK3tu2vQG8J6J5NqjODI

Thanks in advance!