Klam has posted his sample test of Canon 10-22 and Sigma 18-50mm at FredMiranda forum and commented:
“I conducted the test on an overlapping focal length of 18mm. Since I frequently shot my 18-50 at 18mm, I knew I should try to find something wider, which is the reason that I picked up the 10-22.These 100% crops were shot on tripod, delayed timer, RAW straight converted using Canon DPP.
Both lenses are very decent in the centre. The Canon doesn’t seem to show as much improvement and is quite good “wide open” at f/4.0.
The Sigma looks very soft in the corners at f/2.8. At f/4.0 it improves very slightly but still seems soft. Everything is ok by f/8.0. On the other hand the Canon shows a lot of corner detail even at its “wide open” setting of f/4.0. Overall the Canon is a lot better in the corners.”