Purely out of curiosity I tried this combination out the other day whilst out walking about. While it certainly isn't a great combination, in good lighting running at ISO 400 (and later in slightly worse lighting going up to ISO 800) it got the job done! In many cases the autofocus still worked fine when I had time to get proper placement. It hunted quite a bit when trying to focus on smaller targets like slender branches and sticks, but hey getting any autofocus at f/8 is good news to me.
I do have a 70-200mm lens and that with a 2x teleconverter would certainly be a better option, but I guess for those without that option or who don't want to carry that weight and don't mind working with one stop less light, this does work! A few samples: