I am planning to make a deal on a new Kubota 5460 cabbed tractor this week. I have all but settled on how I want the tractor equipped except I have not decided if I want to fill the R4 rear tires..
The cab on a Kubota
L5460 will add about 800 pounds, with most of the weight over the rear tires.
That is enough. I would inflate rear tires with air, the simplest option.
Maintaining traction is usually only an issue with ground engagement work. The only moderately demanding ground engagement work you foresee is pulling a Box Blade. The 800 pound cab will put sufficient weight on the rear tires to maintain traction driven by 56-horsepower gross.
The rear R4 tires on the Grand Ls are, unusually, on two part wheels.
L5460 rear wheels/tires can be spread to any of three width increments: 53.5", 59.4" or 59.1" tread width. Tread width is from CENTER of one rear tire to CENTER of other rear tire. Tread width is published because tire suppliers change tire configurations but tread width is always tread width.
(Perhaps helpful: My one increment smaller
L3560 with R4/industrial tires set at 52.2" tread width has an outside-to-outside tire width of 62". Tread pattern on dirt is 59" wide.)
Spreading the rear wheel/tire stance increases tractor stability more than any other individual option. Consider rear wheel spread first.
Determine max outside to outside tire spread from dealer, based on current Kubota tire offering. (Or inquire here via dedicated new thread.) Buy a 10' stick of 1-1/4" PVC pipe. Cut pipe at max tire width. Mark narrower widths on pipe. Walk around your land, comparing pipe to tree spreads, gates, etc. I did this exercise. It determined I needed a 60" wide tractor. A tractor 66" wide would have been too constraining.
I have air in the tires of my open station Kubota 'Grand L'
L3560. I can pull a full Rollover Box Blade uphill in HST/LOW.