All last week I had a wonderful crush on my EP3. Right up until I used it to shoot some theater stuff at ISO 1600. I also packed an old Canon 1dmk2n in the bag, along with a 70-200 L lens. The focus wasn't an issue but getting really clean, sharp files from the EP3 at 1600 was. (And I didn't expect them to be....).
The EP3 does lots and lots of stuff right. The images, from ISO 200 to 800 are nice and clean and saturated but at 1600 they don't really stand up to the larger pixels on the larger sensor in the Canon. That was my first incidence of dissonance.
This morning (Sat. Sept. 24) I had occasion to wake up my kid at the way too early hour of six a.m. to get him ready and deliver him to a cross country invitational race in Cedar Park, Texas. I packed the EP3 and the same Canon rig again. In bright morning sun both cameras are superb. The Canon is a giant brute of a camera and, with it's white lens on the front, it weighs a ton. The Olympus fits in my hand perfectly and is nearly weightless. But a few minutes of trying to track runners running at speed, coming toward my camera, had me tossing the weightless wonder back in the bag and grabbing for the 2005 vintage sports camera.
The Canon 1d series has three attributes that make it a top choice for photographing your kid running cross country: 1. It focuses incredibly fast. Maybe faster than it's descendant, and with a high degree of accuracy. Even when you are in AI autofocus and tracking. 2. It can shoot at 8 frames per second which gives you options for framing and foot placement of your subject. 3. It has an inherent color palette that works well for sunny and shaded scenes.
The Canon 1Dmk2n is a wonderful sports camera and built to a price point of around $5,000-$6,000. It was almost custom made to do exactly the kind of work I put it to above. The focus is better than anything else I've ever owned, from Nikon, Canon or Olympus. But it's not nearly as much fun to shoot on a downtown street or in a crowded club.
If you only have one camera you'll need to make some practical choices. If you buy some previous generation cameras that are specialized, along with current cameras in other niches, you might end up with the best of all possible worlds. Just not at the same time.