In that scenerio, I might actually opt for a bow and some arrows. If you can't get within a couple hundred yards of a bull in a situation like that, you should find a new hobby. But to answer your question, I'd just grab my 300, and would be comfortable out to 600 yards if the conditions were good. If I couldn't close the gap to 600 or better yet, 200 or so, I'd do a field penectomy on myself.
