I'm going to buy one of these lenses soon. I was leaning toward the Sigma. Have the 60/1.8 and love it, and don't get the sense that the Sony 20/2.8 gets much love. But I do like the size of the 20. So I'm weighing paying more and sacrificing some IQ vs size. So the question is "just how much IQ am I sacrificing if I choose the 20 over the 19"? I may buy them both and have a death-match shootout, but I thought I'd check in with the crew here before another buy and sell adventure. Thanks for any thoughts (or images).