Fenix hit it right on, R4 will last much longer on pavement or hard dirt, gravel etc like on construction job. As for FEL capacity, I have loaded my P7010 with wet clay sand mixture till the FEL wouldnt lift it and the tires have not even bulged. Sure the tires on the R4 are usually higher ply rating but that doesnt mean that you will get more lift capacity with them that R1. The tires arent the limiting factor with a tractor. You sure have to be careful with a FEL if you have the bucket heavily loaded. I had a pucker factor of 100% just a few days ago on mine with a heavy load of dirt that was heavy on the left side, which was also the low side on a slight slope. When I started to dump the load, I hit a small dirt hump that was maybe 3" high. The combo of me stopping, lowering the load, driving on a slight slope and heavy on one side, sent the rear wheels up in the air and tilted to the down slope. Luckily I was low to the ground when travelling with the load and was able to drop the load quickly but it did remind me that I need to load those tires with ballast. Another time a few days before, I was really pushing into a spoil bank loading out some of the same dirt and the FEL wouldnt raise. I had lifted as much pressure as the hydraulics would put out an it wouldnt come up so I decided to just back out from under it. Luckily I kept my foot on the clutch, the front wheels loaded up, sank in the ground past the axle on one side and the rear wheels must have came up 3 feet before I could stop. Of course I didnt have on my safety belt and when I clutched it, my head hit to top of the cab. But again, the tires werent a factor in the loading, they dont show any squatting at all with as much as the tractor will lift and that is factory rated at about 3500 pounds if I recall.
