Very nice lens, Jamie.......every bit as sharp as my 70-200 f/2.8 IS......and, look around for a 1.4x and 2x for it. You'll get AF (with the center spot), and, with any luck, with the 2x as well.
My 2.8 with both convertors stacked (f/8) will actually AF to some degree, if the subject has some...