GK,
I used a 6 foot medium duty KK disc to work up 2 acres for my lawn a few weeks ago. heavy weeds and sod, all mowed short. It was a mixture of soft topsoil and heavy packed and dried out clay from digging the basement. I added a couple hundred pounds to the disc. I made one pass very slow to let the discs cut the sod, then several passes in higher gear. The sod turned perfectly. The landscaper who helped seed the lawn the nest day planned on using a bobcat tiller. He was shocked at the job that disc did. He even said he will look into getting a disc for his bobcat now!