Canon EOS 6D Instruction Manual page 99

If <B> or <M> is set, the time lag from when you press the shutter

button completely until the picture is shot will be longer than with normal
single or continuous shooting.
When the battery level is low, the continuous shooting speed may

become slightly slower.
In AI Servo AF operation, the continuous shooting speed may become

slightly slower depending on the subject and the lens used.
i: The maximum continuous shooting speed of approx. 4.5 shots/sec.

is attained under the following conditions*: At 1/500 sec. or faster shutter
speed, and at the maximum aperture (varies depending on the lens). The
continuous shooting speed may decrease due to shutter speed,
aperture, subject conditions, brightness, lens, flash use, etc.
* With the AF mode set to One-Shot AF and the Image Stabilizer turned off when using the
following lenses: EF300mm f/4L IS USM, EF28-135mm f/3.5-5.6 IS USM,
EF75-300mm f/4-5.6 IS USM, EF100-400mm f/4.5-5.6L IS USM.
i Selecting the Drive Mode
99