What is the general composition of the soil you will be working with? In the extremely rocky soil I have in western WA, I'd be pushing it with a five foot box blade. My 1820D and a four footer does a good job in my applications. My gut is that you would be at the extreme limits of your tractor if you used the six foot box blade. Of course, if all you worked with was sand and gravel and were not doing agressive digging with the tines, you may be fine.