I Have a MF 1835M looking to get a Box Blade. Woods BSS72 or the BSM72. From what I can tell the only difference is 130 lbs. Most talk is heavier is better. Does that apply here.
A heavier box blade is going to be much less finicky in terms of technique required to get it to do its job. I added 110 lbs to my 5' box blade. A heavier blade needs less 'messing with', both on the tractor seat and off. Then there's the durability benefit. Yeah, it's a total win as long as your 3pt can lift the thing even when its packed full of material and get it to dump it out. That's the limit I run into with my tiny B6100.
I have another project tractor with a 3pt that can lift 2000lbs. But, if i hooked a 1000lb box blade to it it might not have traction/power to pull it. Adding weight will make the same width work better, but adding width will make the traction/power requirement go up a lot faster than the weight. You don't want to add weight by adding width. More weight in the same width is good