I am a portrait photographer, working. I have a canon 5D MKii with the kit lens, 85mm 1.8 IS, 70-200 f/4 L IS I am eyeing a new lens mostly for some more diversity in my photography. I am thinking maybe something even wider, and a nice low f/. Or maybe just upgrade the 70-200 f/4 L IS to a f.2.8. Any thoughts? Something else?