I added a Canon 2x Extender II to my Canon 70 - 200 2.8 lens and it makes a huge difference in bringing subjects up close, making it a 140 - 400 mm lens. While it turns it into an f5,6 lens, that is not a factor in outdoors daytime photography. And a heck of a lot less costly than a full time 400 mm lens. The football player was shot at 1/400 f7.1 ISO 1250 from about 200 feet away. He is an 1800 x 2500 crop from a Canon 5D MkII full frame 5616 x 3744 pixel image. Maybe a bit softer than that lens alone but pretty good. Less useful indoors, but the Fall Home Show photos were shot at 1/100 at f5 ISO 2500 so the extended lens would have been quite useable at f5.6. And in trade show and event photography, sometimes the best action shots are taken from further away. And on the factory photography project it will let me get right into that action as well while keeping stuff from falling on the hard hat.
Have to try that combination with video, but only on the big heavy Sachtler tripod to keep vibration down.