Unless you are going to be on fine turf more often than not, I would stick with the R 1's. They are light years ahead in traction when winter time comes, or in muddy terrain.
But, it also depends on where you will run the thing as well. What I mean is, are you going to be on construction sites or other rough places like that, that may have sharp debris? The R4's usually have more plies to safeguard against accidental punctures. I have driven the R1's on my own lawn which I am very fussy about, and on a much heavier tractor than yours (JD 4500 with loader, wheel weights, and rear blade etc) without damaging anything. You just need to be more aware of how you drive the tractor on fine turf with the R1's, and stay off really wet or soft turf with them.