I guess you are running a 50T/13T combo on the 3 speed? If so, I would go with the Mountain Drive. You will get approx 19", 25" and 34" at the bottom end which should get you up most gradients when fully loaded.

With this set-up the top-end remains unchanged, and therefore not particularly tall (mid 80"s?), but you could bump all the ratios up with a 54t ring.