A thought for your while you are considering tire types:
Turfs and R1 (Ag) tires will almost certainly use different rims. If you go to R4's, you might be able to keep your existing rims (not sure what the scoop is with the JD 870).
Either way has it's advantages. If you can use the same rims with the R4s, you save some $$ by not purchasing new rims. You give up some of the traction of the Ag tires, but not as bad as staying with turfs. You get a tire with decent traction, great for loader work, and not as tough on grass or other sensitive surfaces as the Ag tires.
If you go with the new rims and the Ag tires, and keep your old set of turf tires/rims, you spend a bit more. However, you get the great traction of the Ag tires, and can always swap the turfs back on if you have a job where they may be called for.
John Mc