How does the 5D hold up with action shots?
 

Thinking of buying one but I need something for sports and wildlife that involves pans and often times running on a merlin. How does this camera perform in those areas? I've seen some films on vimeo and I have a few worries.

imo,

not a good idea at all, rolling shutter from my experience is pretty unpredictable, can skip/gello at any time,

the camera generally for me is for careful cinematography, does not forgive shaky moves,
I'd think tripod or monopod is desired.

This is the gospel truth. Great camera but quite prone to rolling shutter issues. Longer focal lengths exacerbate the issues too, so best to avoid any bumpy, jittery, shakey handheld anything. Stabilize with a tripod, steadicam, or even FigRig.

I think the 5D MkII can work for action sequences, but you have to plan your shots.

* Pan the camera only one direction per cut. No back and fourths.
* Use wider lenses for faster moves. The skew will blend with the lens distortion, which people readily accept.
* Move the actors more than the camera - especially around buildings and straight lines.
* Pay attention to shutter speed, which isn't easy to control.

There are better cameras for pure, handheld action, but if this is what you have, you can still make it work.