Like some others have already said, looking at your current set up I think you'll probably only be satisfied with the 1.2. If you got the Sigma or the 1.8 I'm sure you'd be able to take some great pictures but you'd always have that thought in the back of your mind that the 1.2 might be just a little better. I love that lens and glad that I spent the money to get it. I don't think you'll be disappointed at all. Plus if get the Sigma or the 1.8 then the new lens will feel left out because it doesn't have a red ring like your other lenses... and that would just be mean.