I'm no expert, so this is all personal opinion, but I think the diameter of the center round and the width of the emeralds is what your eye will focus on, and that already balances nicely with the width of your wedding band, so all you would be doing is adding bulk at the underside with the thicker shank. I also like how the taper defines the last round diamond and makes it stand out more, and you may loose some of that with a wider shank.