I've read somehwere that the 5D mkII focuses slower than other camera bodies by Canon.
Why is this so?? Would it still be slow focusing if you have a 2.8 lens on it??
It has an old AF system--introduced in the 20D. In fact, it has the same AF system as your XTi. It is fairly fast; but is just slightly slower than the current average.
i wouldnt worry about it unless you are looking to shoot mainly sporting events etc. i have one and i have not had a problem with it.
The 5D2 is a studio, portrait and landscape type camera. Its AF performance is absolutely fine for the intended uses of the camera. The image quality it provides trumps most other dSLR cameras.