Columbus isnt all its cracked up to be as a dry hop. I used 2 ounces in a 90 ibu ipa, all can taste is the columbus dry hop and its not the most pleasant thing in the world. It sorta tastes like your eating a hop and not in the way you might think. I'd go all Amarillo... considering you put 4 ounces for bittering, that thing is gonna be all bitter and little aroma from what you said. I'd use 2-3 ounces for 10 days.