I shot my son's soccer games this season with the 70-200 f/2.8 L IS, the 100-400 f/4.5-5.6 L IS and the 70-300 f/4.5-5.6 DO IS, all on a 1Ds Mark III body. I've done the micro focus adjustment of all three lenses on my camera body, which optimizes them. After that the optical quality is very close between these three lenses when shooting raw. If you don't shoot raw you will have less contrast than you would with a non-DO lens. It's not terrible, but definitely noticeable. I usually have to use a bit higher "Blacks" threshold in ACR for the DO lens... like 8 instead of 5 to achieve the same look.
Something to consider that you may not have realized: The 70-300 DO is only 1/3 stop smaller maximum aperture than the 100-400 L in it's range - for example, at 200mm the 100-400 L has a maximum aperture of f/5 while the 70-300 DO has a maximum aperture of f/5.6 at 200mm, so the out-of-focus "bokeh" is nearly identical between these two lenses. The out-of-focus "bokeh" of the 70-200 f/2.8 L is usually better, but depends more on subject distance than lens when shooting sports where you're not entirely in control of subject distance.
The autofocus is a bit slower on the DO than any f/2.8 lens, but I felt it was identical to the AF speed of the 100-400 L lens. The zoom mechanism on the DO lens is also stiffer than the L lenses, so setting the zoom quickly and accurately is either a little slower, or when done quickly (like shooting sports) is a little less accurate.
If you want to see for yourself, I've attached three files, one with each lens. The EXIF data is intact so you can find out which is which, but try to guess before looking.
[attachment=9851:HUBR2121.jpg] [attachment=9852:HUBR3233.jpg] [attachment=9853:HUBR3900.jpg]