07-22-2013 08:51 PM
YES. AF is dependant on both the body & the lens. Another thing that helps speed AF up is lenses which have what's called a Focus Limiting switch. They allow you to stop the lens AF drive from going from 1 end of the AF drive all the way to the other before reversing back. (say the lens can AF from 1 meter to infinity the switch can be set to stop it from searching below 6 meters before starting back towards infinity). Generally speaking L series lenses AF noticably faster than consumer grade lenses.
07-22-2013 09:39 PM
07-23-2013 12:32 PM
Lenses with "USM" in the name indicate that the focus is driven by Canon's Ultra-Sonic Motors. There are actually a few variations on USM, but they're generally fairly fast (noticeably faster than non-USM.)
Not all focus points are active at all focal ratios. Generally the more light the lens can gather while focusing, the faster and more accurately it can determine if it is focused and additional focus points may come into play.
Lastly... if you're hand-holding the camera with a lens that has image stabilization, then even if you're shooting action at high shutter speeds (fast enough that camera movement wouldn't be a problem) you should _still_ enable the image stabilization. That's because the camera can lock focus faster if the lens stabilization is enabled.