The old phrase "Different horses for different courses" certainly applies when choosing tires.
R-1's have a deep, biting tread pattern that is designed to find traction in soft fields.
R-4's have a wider, flatter bar tread that sorta works on off-road applications but also provides reasonable traction on hard surfaces such as asphalt. The R-4 is a compromise tire that tries to work well in all situations but doesn't really shine in either one. But the tread design will last longer on hard surfaces than what an R-1 pattern will and that's one of the reasons they are used on construction machinery.
Bottom line here is YOU. What are YOU going to use this 444 for? If it is going to spend most of its time in the garden or in the muddy woods hauling out firewood, then R-1's are the best choice. If you won't be running in mud or the garden, then the R-4's will work fine.
I have no suggestions about 16" rubber. Skid steers use 16.5 or 15". Maybe you will have to find some 15" rims with the correct offset and bolt pattern if you want to run R-4's.
