also keep in mind if you are shooting with indoor lighting at 1/50th in North America there will be flickering in your footage due to the electricity cylcing at 60hz. (fluorescent or mercury vapor lights) this is because your shutter is out of sync with the electricity 50vs60. so yes, solve it by shooting at 1/60th in these conditions, or 120 etc. if you're going for a specific look. As background, I film freerunning/parkour with my 5DmkII and personally, prefer shooting at 1/125th vs. 1/50th for the action. Shooting at a higher shutter speed is also necessary for "twixtoring," although I don't recommend twixtoring any of the footage from the 5d as, discussed earlier, it's limited to 30p. But shutter speed affects video the same way as photos, if you think about it its just creating 24/30/60/x stills and putting them together in a 1 second time window. good luck with the filming, and if you do try to twixtor with your 60p footage, make sure you are shooting over 1/500th shutter speed and have a plain background (sky, out of focus, etc), and don't allow your subject to move their arm across their body. difference would be - a decent usable twixtor - guy walking towards the camera with arms at sides, no overlap of body. bad twixtor - guy walking past the camera left to right, a lot of overlap of swinging arms. If you visualize your scene in 2D, it is a lot easier to determine how your footage will turn out. I always try to focus on the end goal when I film, and especially with high action shots like freerunning its hard to get things right consistently. good luck!