The X10 is very good for street photography and the X20 will be too, but I never used AF for it. With its relatively small sensor, it has all sorts of DOF even at f4 or so. I always used it with zone focus and never worried about getting focus right, just getting the moment right. Very easy to setup for it. Not quite as quick as a Ricoh or the LX7, but plenty workable. That's the way I use my OMD and X-Pro for street shooting too - I find AF to be a really distracting extra step, no matter how fast it is. These are examples from the X10.
Yeah, for sure if you like to shoot street at longer focal lengths, that's where AF becomes pretty critical. I rarely go longer than 28 and almost never longer than 35, so I just stick to zone focus. Which works better for me at closer quarters anyway.