I have R4s on my Workmaster 40. I HATE them. They are 6-ply rated and extremely stiff which is great for resisting puncture.
But, this lack of flex also causes them to have very poor traction. I find that they are so bad that I have to keep my tractor in four wheel drive almost all of the time, even when driving on gravel hills.
I really wanted R3s again because that’s what we had on our previous tractor and they were amazing in all conditions. But, R3s are nearly impossible to find around here on new tractors, and dealers tend to shy away from swapping them out for you when you buy. If I could do it over again, I’d demand R3s or no sale.