I use Johnson's Paste Wax on my cast iron, and have done so for many years. I've tried other products, but have always gone back to Johnson's. My shop is less than 50' from a lake in North Carolina and any iron without wax rusts very quickly in my shop. I usually re-wax all of the tops when doing my quarterly (roughly) tune-up, but also re-wax any time that I notice that wood doesn't slide easily. I have never had a problem with the wax causing finishing problems because when I apply the wax I wait a few minutes and then buff all of the excess off. I also sand all of the surfaces of my projects before applying finish, so this removes minute traces of the wax, if there were any. I also use Johnson's paste wax on the ways and gearing of my Unisaw because it does not attract and hold sawdust like other lubricants. An old toothbrush is a great applicator for doing this and I leave it thick here with no attempt to remove the excess.
Charley