Focus accuracy question

I have a 7D with a 400 5.6. I was wondering if there is a difference in focus accuracy while shooting in AI servo while setting the drive mode either to low speed continuous or single shot and then only taking one picture with the subject not in motion?
I usually leave it set to low speed continuous just in case I need to take multiple shots relatively quickly but I have heard that sometimes in continuous mode the first picture taken may not be really accurate as far as focus is concerned or is this not a factor on a stationary subject, birds, in my case? I wouldn't think it would matter on stationary subjects but I can understand it possibly coming into play on BIF. I could probably get by with it set to single shot most of the time but occasionally I do get a bird hopping around from branch to branch and I like to be able to follow it quickly while holding down the back button focus and that's when low speed continuous is nice.
Any opinions are welcomed.
Thanks.

CFn III-2 will determine whether or not focus has been achieved before the first shot is taken when you're using AIservo.
Set it to 0 or 1 if you want to wait until focus has been achieved.
Setting it to 3 or 4 will fire off the shot as soon as you press the shutter release.....focussed or not.
(see page 210 of your User Manual)

Bob