So much depends on whether the dog is inside or mostly outside and of course his nutrition. Some wire coated dogs take a long time to dry, so with ours, we have tended to wait until his whites look grubby and/or until we have noticed his doggy odor (which fortunately is not that often).
I think it is very important to use a gentle dog shampoo. You can check his skin condition in between bathing as well to make sure that here is no flaky appearance or no agitated redness anyway beneath his coat.
It all depends on the dog's coat.I've found both powders work well on short coats; but the baking powder probably works more effectively on medium to longer coats. (Needs to be brushed through thoroughly, particularly if coming inside afterwards.)