A shutter speed of 1/80 would not generally be enough to use the 70-200 and get sharp photos. Especially if you use it on a crop body. F4 200mm has thin depth of field no matter though. Heck I go to f8 quite often at 150ish mm to get enough depth of field and that is where the IS really shines.
The bokeh difference between various lenses can be down to far more than the aperture used though. The entrance pupil will affect the shape of the bokeh even at the same focal lengths and aperture. Bigger front elements do better. The f2.8 will also focus quicker in worse light and it will let the camera activate more cross type points. There is no question that the 70-200 f4 non-is represents tremendous value though.