Now the optical performance: As I have clearly runtergeschraubt my expectations, I was very pleasantly surprised. The sharpness is really good, even already at full aperture. Even sharper it is, if you stop down a bit and the image stabilizer off (!). That actually brings a distinct focus and advantage in the modern sensors with the already dizzying ISOs feasible without much noise losses.
A chromatic aberration etc. already visible in details such as fur structure, but can be very easily calculated out automatically and with a high quality visible gain in raw performance demands with the grand Canon software (Update!). The bit more work I take willing to accept, because I get a very flexible and outstanding good in this price range lens that the wallet and easy on the shoulder.
The attached photos were taken under cloudy skies on our balcony with 250mm, maximum aperture and without image stabilizer