I like the pose, this fellow has a great head angle considering his back is to you. Your image is pretty sharp, but maybe another round of sharpening on the bird would help. The light is very harsh so you've lost detail in the blacks. I'd suggest trying to tone down the background, and do some noise reduction on the background.
The grain is actually noise, and may be showing this much either because you've made a pretty substantial crop or the image was underexposed. In any case, if you select only the background on a separate layer, you can then run noise reduction either with Lightroom, Photoshop, or some 3rd party plugins such as Neat Image or Noise Ninja.
Do a search on shooting to the right. That is, using the histogram to maximize the capture of good data. As far as I am aware, digital sensors capture the most data in the highlights and not the darks, hence pushing to the right during exposure, then pulling the exposure back in post can yield very good results with regards to noise. I have written a simple tutorial on my blog a few years ago using an even older camera. The technique works.
Another reason for noise as mentioned is a heavy crop. Getting as close to the subject is the best thing you can do for image quality and detail. Nothing can improve good field craft. :)
A cleaner background would've been ideal. Nice head angle on your shrike.
Gianluca your 3rd version is better. I agree entirely with the tips comments mentioned above, I had a 7D for several years and was very pleased with it, I was always pushing the exposure to the right and trying to minimise cropping, indeed this advice is goos for all cameras. Possiblyt your image was initially slightly underexposed and you have a fairly large crop. I suspect you were perhaps concerned not to blow the white plumage and the pale perch. On an image like this I would have tried to get the exposure so that there were blinkies just appearing on the white plumage. I refer to the image in the back of the camera, remember this is a jpeg so when you process the raw file you will be able to make some recovery. I would be less concerned about the perch as this could be modified in a variety of ways, even brushing lightly with a grey brush.