Sigma 10-20mm F/4-5.6 - good copy ?

hello forum experts,

I need your advice!

I recently got a wide angle lens to "complete" (is there such a thing?) my setup based on a 40D: 17-55 2.8, 50 1.4, 85 1.8, 70-300 4.5-5.6. I am not a professional and I am quite happy with the "second best", non-L lenses available. The Sigma 10-20 4-5.6 seemed to be an excellent value based on many reviews and comparisons I read online, and a very useful and fun lens. I'll use the lens mostly for landscapes and for some playing around. No special indoor photography is foreseen in the near future.

A lot can be read about the quality control issues of sigma lenses, and bad copies of this particular lens. When the lens arrived a few days ago, I started to do some tests. These included shots from a tripod outdoors and indoors, which showed pretty good sharpness overall, but with a somehow soft upper left hand corner.

Today I took some shots outdoors, wthout tripod but with sufficiently short shutter speeds. These shots were not particiularly sharp at all (the focus is somewhere below the boat in the center), but that was not the issue anywaysy. The feature that was more important to me is the upper left corner which is way more soft, than the right hand corner for example.

What is your opinion? Is this a bad copy of the lens, or is it within specs and something that you would consider OK ? I never did a thourough lens test and I don't know what I could possibly expect. And "yes" I realize that the pictures I attach below are "quick an dirty" tests taken whithout much care, though I think that they might allow to judge the critical point, at least in combination with other shots that showed overall excellent sharpness. It's the corner performance that is most worrying me.

BTW, I did not see any of the much criticized flare, not even when pointing (almost) right into the sun wide open. CA is present though, but reasonable.

The pictures below where taken at f= 4, 5, 6.3, 8, and 11, at 10mm, handheld. What's the verdict, OK copy or not? Or is there more and more serious testing necessary?

f=4 at 10mm

f=5 at 10mm

f=6.3 t 10mm

f=8 at 10mm

f=11 at 10mm

Thanks MUCH in advance for your help !