The feathers would be less dense so their center of mass would also be further away from the person holding them horizontally (unless they were hoisted straight up over the holder) and thus require more torque to keep from toppling over.

But also being less dense but the same mass the feathers would displace more air and thus have more buoyant force on them, so even though they will be no less massive they would apply less downward force.

So I think the conclusion is that for steel and feathers of equal mass the feathers would be less heavy but require more strength to carry.