Sure Al, and a point worth adding is that weight in the tyres/wheels does not give extra wear and tear to the tractor, like carrying a weight on the 3 point likage can do.
When I was invovled on farms it wasnt uncommon to fit dual wheels for land work, fit cast wheel weights and fill the tyres. The "less flexible" issue was always noted though, and the filled tyres never seem to get the same traction. Perhaps when "carrying" the extra weight, that weight was pressed down on the ground via the rim, therefore forcing the tyre to flex. Not sure really but filled ones always seemed "harder" even with the same pressure in them.