<font color="blue">What do you mean when you say "you agree it's a weight issue"? </font>
Just that the heavier a machine will disturb the ground more then a lighter machine with a similar tire type. I use AG style tires on my garden tractor and it can travel across the lawn without damage. It all comes down to ground pressure which is determined by how much of tire surface is in ground contact and the machine’s weight.
We tend to think of this in static terms, measure the tire PSI at rest and that’s the ground pressure. But this ignores tires don’t have a uniform surface shape. The surface area of a rolling tire in contact with the ground varies instant to instant during the revolution. A slick tread tire has essentially the same amount of tire surface in contact during the revolution. As the tire tread becomes more radical the greater variation in surface area during its revolution. This lets the tire “dig in” and creates more traction with aggressive treads.
In your last post you were asking about possible damage to tree roots from soil compaction. Neither tire style will be an issue with trees; below the first couple of inches from the surface they will cause an equal amount of compaction. As the various posters have said, R1 provide more traction while R4 cause less surface disturbance. R4 usually have thicker sidewalls making them be more puncture resistant. Either will work for you, the differences are merely a matter of degree. But for the tractor and the uses you described R1, in my opinion, is the better choice.
<font color="blue">Unless there is a lot of rain, the clay soil in my area stays pretty hard packed </font>
Late winter and early spring, in this area, are often the worst time for wet soil conditions. Usually there are several weeks when the ground is thawing on the surface but still hard underneath.