The IS is a great combo with the MK3, I've used it with fantastic results in clarity, color, and bokeh. I would warn that it is noisy (audibly) and may be particularly unsuitable for video.
case and point with this shot. your shutter landed at 1/800 @ F/4. you were twice the shutter needed at 200mm to hand hold the shot for sharp results....IS made no difference in getting the shot at all. A 70-200 F/4 non IS would yield the same results. If you were inside and this landed at 1/100...then an IS lens would allow you to hand hold and get the shot
However, your ISO was at 100 ISO....you could easily raise the ISO to 1/1200-2000 and get the same results inside with out compromising image. 2000 ISO is very clean on a 5D3.
being aware of where your shutter is at and controlling ISO is the key to using a NON IS lens.
Shooting in TV mode, setting ISO on auto, setting shutter speed parameters to 1/500 puts the camera in a safe zone to capture images. Save the settings in C1 and you are set.
IS lens are great to have. But knowing the work arounds with your cameras, especially on these very clean sensor cameras will save you a lot of $$$ on your glass investments
