Well, I tried using both cameras yesterday for the first time during a high school soccer game. I had my Canon 20D around my neck with a 70-200 mm f2.8 lens and my Canon Mark II on a monopod with a 300 mm f2.8 lens.....a little challenging to say the least.
First, I take care of my equipment really well, but with 2 cameras running at the same time, there's a tendency for them to knock into one another. Second, trying to change the zoom on the 70-200 lens while still holding the monopod became quite difficult, leading to several missed shots. Here are a couple shots from the 2 camera/lens combinations......both with wide open aperture of f2.8, shutter speed ranging around 1/4000 sec and ISO 400. If you would like to purchase any of these game photos, please visit my Smugmug site.