I have a heavy eight foot rear blade for two reasons. I have my rear tires set out at their widest( 80" - outside to outside) and blade weight. I offset the blade to the MAX when I clear out my driveway ditches and clear snow off the driveway.
Some here on TBN use the next size bigger( 108") on my size tractor. My Kubota Op Manual says - max is 72". I do some pretty heavy grading with this rear blade. I don't think I would ever need anything bigger than what I have.
I don't feel I need to find what the absolute max is by breaking/damaging equipment.
I don't think I will EVER get good enough with my rear blade to equal what my land plane grading scraper can do.
Unfortunately - each implement ( land plane grading scraper vs rear blade ) is best for specific jobs. The LPGS will smooth a driveway - like a babies butt. Mine has scarifiers - so I can easily get rid of potholes and the like. However - it won't do much else.
A rear blade is a truly multi-use implement. Grade material up out of the ditches - spread it across the driving surface - reverse & drag for a truly smooth surface. But it's not really the implement to repair potholes and the like.
If you get a rear blade - look for one that will offset - angle - tilt.
My LPGS is out in the weeds and between some of my smaller pines. It's "day in the sun" is rapidly approaching.