I think the important thing is to note that today's diesel (US) is NOT the same as diesel from even 10 years ago. I believe most offroad diesel is now or will soon be ultra low Sulfer, just like on-road diesel has been since ~2006. My understanding is that sulfer was a major contributor to the lubricity of diesel, similar to lead in gasoline. When you remove most of it, the diesel does not lubricate the pump like it used to.
Newer tractors should have pumps that will last OK with ULSD, but older ones do not, and there will be increased pump wear because of the "dry" diesel we now have. IMO, some sort of lubricity enhancer is not a bad thing for older tractors. There have been studies done as to which additives produce the best results, and you can find them and read them, but the interesting thing that I came away with was that no additive improved the lubricity as much as even just 2% biodiesel.
The biodiesel I am talking about is NOT waste veg oil, or some hillbilly junk your buddy runs in his old Cummins or Mercedes. I am talking about B2 or B5 that you can get from many reputable stations. Unfortunately for me, I haven't found any around here, so I use the white and silver PS in my truck and my tractor most of the time. It's not the best product, but I've never had any gelling problems, and the truck has 240k miles and still runs great.
I have used 911 twice when I had a gelling issue after a night of -15F temps on a tank of mostly #2. It worked almost instantly to clear up the fuel and get the trucks running. It is a lot of alcohol I think, not good for your system, so emergency use only. The white bottle does have some alcohol too, which will combine with any water and run it through your injectors. This is also not good, but perhaps a necessary evil in the winter in some places. The silver just adds lubricity, so should not have any alcohol. If you use diesel #1 in the winter, it shouldn't gel till it's below zero.
I highly doubt the additives do much for soot, or how an engine runs. There's just not enough to them. (They don't even do much for lubricity, compared to bio...) Quality of fuel, tuning, amount of work done, idle time, etc are far bigger contributors. FWIW, biodiesel also has a more "detergent" effect, so if you run a lot of it in an old fuel system that's never had it, it'll flush a lot of gunk into the filter. It's not the bio that's clogging the filter, it's the junk left from years of dirty fuel...
Good luck.