Going back to what other's have said regarding floatation vs. traction. I think it's important to remember that while the R4's offer better floatation, this is due to more surface area in contact with the ground. This situation is great for lawns and roads as the tires will wear less quickly.
On the other hand, the R1's are designed so that there is less surface area and therefore, the force is spread out on a few lugs at a time. This gives very poor float (they dig very fast...) but in mud, they tend to dig sink through the mud to the solid ground below (if there is any).
Farmers use the R1's for a totally different reason than either above. Since they are mainly using their tractors in loose dirt and field work conditions, they want a tire with the most surface contact they can find. Since the lugs of the R1's dig in to loose dirt, you are really getting surface area on not only the bottom of the lug but on the rear side of it as well. Therefore, you actually get more surface area from R1's in loose dirt. (Actually have talked to the farming neighbors about this) This is also one of the reasons they like to load their tires. If they don't sink in a little, they get very little traction.
The worst conditions for R1's are ice. Very little surface area and the tires can't dig in like designed. Quite dangerous.
In my opinion, the reason many people don't see a difference between R4's and R1's on CUTs is that the tread on the R1 isn't that much deeper than the R4 tread. When you move into a bigger tire, you get a much deeper (4 inches +) lugs. Many farmers replace their R1's when they reach about 1.5 inches of tread left around here. It's just too wet to have that little tread and pull a fully loaded wagon.
Just some food for thought!!!