The Minolta 28-75 f/2.8 uses the same optical design, don't know how similar the specific elements are and theyre coating and such. I love my Minolta and corner sharpness is even good to great even wide open. The only time you hear anybody make even a moderate complaint about corner sharpness on this lens is because they are using it on full frame, APS sensor has a great sweet spot with this lens, certainly worth it. Look for the Minolta version, should go for about the same price, or you could also wait for Sony's version to come out which I believe has the SAM and the zoom lock tab.

Though you do already have great portrait lens, this is another great one with an extra stop of speed. On mine the color is also slightly more neutral than my other Minolta glass.