Just got back from a soccer game. Inspired by this thread I actually tried the 5D II again. I should have listened to myself and not done that.
I only shot ~35 images before I gave up. About 50% if the images are unusable due to AF tracking (or lack there of). With the 7D, it's maybe 1% if even...
Show me a burst of 5 images of a runner/dog/vehicle coming STRAIGHT at you at > 5 mph. I've not seen it happen and I *OWN* the 5D II. I'm not dissing it from a distance. Lateral motion, panning etc, sure, that's easy. The focal plane isn't moving much. Back/front is where the problem is.
Yes, people have shot sports before there were "proper" AF cameras, but that doesn't mean it was any fun! People also drove cars without seatbelts, synchronized gearboxes and power steering.
Anyway, I already made up my mind (AND put my money where my mouth is), but my simple advice would be: If you shoot a sport that requires actual (non lateral) motion, the 5D simply sucks at it. Go get a better body.