This suggests it WILL be prudent, and safer, to fill rears?
The MX5800 is, in my opinion, inherently more stable than most due to its stance, fat tires and weight.
I am on my third tractor. None have had filled tires. I prefer the flexibility of selective Three Point Hitch ballast.
I do not have any sloped ground to work in Florida. If you have slopes to work in Wisconsin, perhaps filled tires are advisable as they lower the center of gravity. But I would explore adjusting the rear wheels wider first.
In MY conditions, with R4/Industrial Tires and 4-WD, I have never felt the need for more traction, the second reason for filling tires. See Photos #4 + #5. Those rippers are in the ground a full 10". Four wheel drive is effective.
I try NOT to compact the soil with passage of my tractor. Most of us operate over the same ground regularly. Compaction takes decades for Mother Nature to ameliorate. Plowing only submerges the compaction 8" deeper.
Soggy Water Oak in Photo #1 + #2 weighed around 1,600 pounds.
MX5800 = nice tractor. You will love the telescoping Lower Links and pinned stabilizers when mounting implements.