I asked these guys the same question, and eventually settled on the 48" size, and I ordered a Kingkutter 'cause it was low priced and built well enough for the horsepower I have available. It arrived Friday, the ground is frozen so no performance report yet. However, here is my rational: I bought the box blade for several reasons, one being for the heaviest ground engaging dirt moving. I realize from past experience that the loader bucket is not the right tool to do landscaping on flat ground, it won't bite into the normal soil surface or turf. I have a building site to level which contains tree roots and the box blade will start there. Second on the list, I needed loader ballast. Someone on this list said, "yea, if you can get an attachment that actually does work and use it for ballast too, that sure beats a box full of cement or rocks". So I got the little box blade home last Friday and by Saturday afternoon I had a 360 pound slab of steel plate bolted to the back of it. Now I have about the correct loader ballast (box blade is 350, total is 700 plus with hydraulic top link). The three-point has no down-force, so the extra weight on the box will help make it more effective, and I can lift it if it wont pull, then some of the weight goes onto the tires, so that'l help too. Incidently, the box blade measures 49" wide, which covers my 4100 rear tires nicely. Since it is just as wide as the tractor it is not a big nuisance back there as a ballast. If you buy a bigger one, plan on a ballst box also 'cause it will limit your manuverability if wider than your tractor. It is also a great idea to lower it to the ground if you are stationary and lifting and want tractor stability, like having a huge anchor. Lastly, the horsepower question comes into the equation. Part of the deal is also weight, because if you don't have the tractor weight you cant get the traction to the ground to pull the box. But assuming you can ballast the wheels to pull the box you buy, the horsepower then determines the RATE at which you can do the job. If you buy too big a box, you can shift down, lift the box, lift half the scarifiers as mentioned in previous post, etc. For a box blade this should work just fine. For certain tillage tools it does not work to slow down as you will then lose "action". Like a field digger, you want thengs flying around a bit. One more thing, the smaller ones are usually cheaper, but lighter weight. Then you can beef it up where needed. I plan on adding some sacraficial plow shares on the side plates, to beef up this wear-prone area (presently it is 1/4" material). Good luck, try one out first if you still have doubts.
