16-35L II vs 16-35L f/4 IS?

only reason i'd even consider the 2.8 is if i shoot events and need the shutter speed, also astro, but then again i've had great success with my 16-35 f4 for milky way

the f4 is cheaper, has better IQ all around, the IS is more useful than people give credit, for example along with landscape i shoot a lot of food, often need ~f/4 for the depth of field anyway and the IS allows me to get sharp shots quite comfortably even at 1/10 ss at 35mm which is great for those low light venues

".....but likely at F5.6 on a tripod there would be no difference."

I owned the 16-35L II for many years. I sold it for the 16-35L f4 IS. the f4 IS will be sharp across the frame at F5.6 and the f2.8 II will not.