Stills IQ only...500 vs 550

I'm looking for a new DSLR (moving over from Pentax K20). I've looked at the Nikon 5000 and the Pentax K-r, but hear such good things about the EOS series I thought I should come over for some user advice.

I'm not all that interested in video, stills only, and then usually still life or street scenes and usually in B&W. IQ is far and away my main concern, so can I get the same IQ from the 500 as the 550 with the larger sensor and video enhancements I don't need? Thanks for any feedback,
Brian