On more fundamental differnce to point out which I read some where on this board that I didn't even think about until he said it: if you add weight to the 3pt or the wheels, you are adding stress to the tractor axels, frame, etc., compared to filling the tires where the weight is always at the bottom of the tire and adding weight to the tread only. I personally added weights to my tractor simply because I did not want to mess around with filling, repair issues, etc., thats not to say it is a bad idea. Also think about the location of the weight when on hills. In the tires that weight has a very low center of gravity. When it is on the axle or 3pt, you have raised the COG and now changed the stability of the tractor. I was really concerned about this at one point because of my hills. But, as it turns out, when I am on side hill that is just a little too much while mowing and loader down as far as possible, the rear of the tractor will start to slide slightly. Thats when I know I have gone too far. But, I would rather slide than tip! my personal opinion is that the extra weight is what makes it slide as opposed to getting tippy.