.357 4" or 2" barrel?

Is there a big difference in velocity between a .357 2" barrel and a 4" barrel, I haven't found any numbers on it. The idea is I'd like a light .357 in the unlikely event of meeting a cranky bear (hopefully even so a blackbear of smaller size than a kodiak). Where I usually pack in Idaho, I've never heard of a grizzly being in the area, but I have heard of black bear being around. The only reason I like the 2" is its weight and cost. On a 5 day pack trip, everything, including that extra roll of film you packed seems to add up.