the old doors on the barn (still have one of them on the building) have round rail, besides drilling a hole in the top of it to be able to oil the rollers from time to time it has done well for over 100 years and the granary was put up in late 1930's and it is round and has done well, (drilled so I could oil it as well) one thing I see about the round is dirt will work it way out of it, the box I have seen has lips on the opening in the bottom and besides the ends I see no way of dirt working it way out of it, I did have a door with the boxed rail and it worked good until we replaced the door it self,
for that small of doors I would consider roll ups as well, but do under stand the cost aspect,
on the 9wx7H door the roll up door may be cheaper than materials and the rail/track, and rollers,
the taller unit will set you back some but in time putting a power opener on it is nice, (I am dreaming of my own some time), if your openings are not all ready built checking with a door company you may be able to get some sizes lower cost than others if there not Odd sized, and then construct your openings to those sizes,