The amount of tread you need is dictated by the surfaces you intend to ride on. On the road, slick or very lightly treaded tyres put more rubber to the road and are faster as well. On loose surfaces you're going to need something that digs in and generates a bit of traction. Only you can judge whether the surfaces you ride on are navigable on slicks. There are plenty of touring tyres like marathon supremes that can handle some unpaved surfaces but roll well on the road, have a look at them.