You mentioned that you want to do "longer tours". I suggest you stick with the drop bars since it will give you three effective hand positions which are two more hand positions than a straight MTB bar. Your hand will be less numb at the end of your tour.
Of coure, you can get a straight MTB bar and add bar ends for an additional hand position. Still not as efficient as drop bars for distances longer than 15 Miles.
Cro_Moly_Body