Just got my new 24-70 F2.8L II today!
I ran some simple focus test for fun.
I took a photo of my studio with available light. Handheld 1/160 F2.8 ISO 800.
Single focus point on the red lamp in the center of the frame.
The out of focus "things" on the image are an Ikea lamp in front of me. I did other test shots for sharpness and bokeh.
The bokeh is just a little smoother on the new lens but almost identical... You can see the lamp on the last attachment.
First thing you notice is how much brighter the new lens is. Look at the tufted white pattern on the right.
Then at 100% you really see the difference. Notice how much sharper everything is.
At first I thought I could add some edge sharpening to try to match, and it does get better but adding sharpening also adds noise and artifacts. So a subtle sharpening is fine but it won't match the quality of the new lens.
Color seems similar although I noticed a lot less Chromatic Aberration on the new lens.
I will do more tests when I can. This is a simple, good start, I think.