Yes, it look very weird for you. It should look like this:

I can't imagine what happens to be so dark...

That arfifact is a well known texture projection artifact, and should disapear increasing the pssm_bias value.

In my old NVidiaGTX285 deferred shadows runs over 60 fps, and object shader shadows below 20 fps.

It is not concibed to run smooth, but to remark the process timing difference. Ity renders more than 1 million polygons indeed!

Does your graphic card support sm3.0?