Take a tractor with a loader and a bucket and have at it. Take the disc to it only once if you feel the need to break it up a little, but there's no reason to over analyze this task. I've removed tons and tons of sod with a skid steer and a bucket by just peeling it up once bucket at a time, it's not rocket science. Just under 4,000 square feet won't take more than half a day to remove, if that. The box blade requires you disc the hell out of it, which will create a whole wad of tiny pieces of sod. Then you're going to drag them all over the place? What a mess that would make. Don't make the material any smaller than necessary to remove it, you'll only create more work for yourself if you do. On top of that, the box blade doesn't get the material into a truck so all you're going to accomplish is dragging the chunks off the grade and placed somewhere else where it needs to be bunched up and loaded out. Go with a bucket, it will be the fastest, trust me.