Your photos from Daytona are nice. Great light in all of them. There is nothing wrong with the cropping of your images. Those that pay to have the logos on the side of the cars like to see them, and see them as sharp, and large as possible.
In your pan shots, I'm not sure at what ISO you had your camera set at, but you list a 5DmkIII and a 60D as your cameras. I am not familiar with the ISO capabilities of the 60D, however, the 5DMKIII should give you excellent ISO performance. I suggest you bump up the ISO on the camera while shooting during the day as it will allow you to get better depth of field. If you're shooting at 2.8, 3.2, 3.5... you will have part of the car blurred, especially pans at 1/100th of a second or below. You need to be at about 8.0 to start to get decent depth of field. This also holds true for head on shots.
The other thing is, you make due with the equipment that you have, however, shooting with a 5D, 5DMKII, or 5DMKIII is not the best option, especially if you are shooting raws. While the 5D series are superb cameras, it makes no sense when shooting motorsports. There are not enough focusing points, the focus is woefully slow, and it shoots a little more than three frames per second which is like watching grass grow. Compared to a MK3, MK4, which is at about 10.5 frames per second, or 1DX is at about 12, factor the frames per second, your work output is increased by a factor of three to four times. Having said that, your pics are nice.