The review I've just read suggests that it's soft at the long end until you hit f/8 and over which means you're going to have to shoot high ISO if you're after moving subjects.
I'd be very surprised if AF continued to work with a TC fitted although it depends what TC you are using. The x1.4 will probably be all right, the x1.7 might just work but the x2 usually need f/2.8 lenses to AF