Go w the heavy use or even a little larger. Your condensing temps are going to be high. You have an old box so infiltration and poor insulation are factors. And most important it is beer and beer must be kept COLD!
Seriously though beer coolers are often run at temps below freezing. Beer can tolerate 25-28 degree box temps and customers like it that way. Oversizing a little lets the unit defrost on the off cycle which will help in your humidity, but I would still add a defrost timer to be safe. If they are keeping produce with the beer then your design evap will be about 25 degrees, but if beer alone or fresh meat figure 15 degrees. (10 less than the box temp.)