Just the other day, I broke close to a half acre of hayfield sod for a small stand of corn I want to grown next year. I used a Kuhn EL 62-180, which is a 60 inch, pretty heavy duty, gear-driven tiller. I was impressed. It's a little late in the year and the ground was quite moist. To boot, I have a heavy clay loam, and there was a good 6 inches of grass. I had the wheels set just a couple notches down from the highest (most shallow till) point, and the rear hood up quite a bit. I couldn't go very fast mind you, but it did a great job on just the first pass. The sod was completely chopped, and I had what seemed like a good 4 inches of reasonably fluffy ground. If it doesn't get too much wetter, I'll go out there in a week for a deeper 2nd pass before winter sets in. They say the depth range is 7 inches, but I bet it'll go considerably deeper than that when the soil is worked/softer. From my extremely limited experience, I'd say that a heavy duty tiller is certainly capable of doing the work of a plow and harrow, but only at a "hobby farm" scale. Also, I think it's true, you probably can't beat a tiller for creating a nice, perfectly smooth, fluffy seedbed.