I think for actually moving dirt, your current tractor is the minimum I'd want for a 6' box. I guess a smaller tractor could use it to push loose gravel around but you might do a lot of scarifier passes to loosen things up and then use the blade to move material. I've got a hydraulic top link and tilt the box to use the scarifiers alone. I use the technique to break up compacted gravel or start off in dry clay sod busting. I guess you could always try the 6'er and if its too much get a smaller one.
