here's a sample pic i took with my sigma lens yesterday, full zoom, macro mode, hand held, resized and sharpened, and contrast messed with.
http://picasaweb.google.com/teh.JDog...02293039080546
not as sharp as it would've been had i been using a tripod, and the only other photo out of about 20 of this flighty creature that turned out any sharp.
stupid low light!
i do believe (form what i've seen in online tests and reviews) that the APO is somewhat sharper and has less CA at the extreme zoom end.
either way, i'd definitely buy a sigma lens again, fantastic quality for price.