Depending on what you want to do, the soil, number and size of rocks and roots you may want to get either medium duty, heavy duty or industrial.
Medium duty is about 125# per foot of width, heavy duty is about 150# per and industrial is over 150. No, these aren't some spec, just my rule of thumb to quick check. With the power of the tractor, a good target weight is 150# per foot, anything less and you may bend it up.
Go to woodsonline.com and visit the industrial scrappers. They will be the top of the line standard.
jb