Regarding low light AF, I'm accostumed to the very robust EOS 5 AF, and just recently was able to take my DRebel to a trip and shooted in low light situations (as in church interiors) in where the EOS 5 had no trouble. It was like I've never changed the camera
The Drebel AF is as good as the EOS 5 one, and I never missed a shot for AF issues, and I wasn´t using the flash as AF assist, even at very low light levels (1/6s f/4 at ISO 1600 shots). The 10D has exactly the same AF system, so I think it will as good as the DRebel one.
But if you want the best AF you can get (mostly in AI servo), and more than 3fps, your only chance is the MkII. And the ISO noise is even lower in the MkII than in the 10D.