What kind of planter do you have? Each row unit will have a certain amount of torque associated with turning the meter assemblies. Finger units will take quite a bit more compared to say, a White meter. Those motors you linked, are only 333 in/lbs continuous. Thats something I would look into.

Thats a lot of money to invest in motors, not to mention hoses, fittings, valves, etc. Couldn't you accomplish the same thing with row clutches?