@weeder after reading all of the different opinions and almost no two alike, I'll repeat my comment from earlier in the thread. You have to try things and see what works for you based on your climate, driveway, and needs in general.
I've plowed driveways with chains that I couldn't have plowed without chains. I plowed driveways with R4s with success. Your tractor is light, so the guys who are plowing with heavier machines with loaded tires will have a different experience.
Your tires are small, loading them will get you maybe #100 lbs of ballast. You need weight on the back with R4s just not so much weight that it makes your front end light. Again, experiment with that. Easy to add, remove weight as necessary. Wheel weights is also an option for weight but not sure how expensive they are.