Christmas brought me a 70-200 f/4 IS and I've been wondering how good it would work with extenders.

I don't really mind not having autofocus, so even a 2x extender would work for me, but I'm not sure I'd need it. I do have a 1.6x crop body, so the lens does go up to 320 FF equivalent by default. I mostly take pictures of people (not wedding), and outdoors shots, be it nature or city. I don't really take bird or wildlife pictures unless the opportunity falls into my lap.

Has anyone had experience using extenders with this lens? Would I feel any difference between generation II and III extenders (apart from the price of course)?