The only time the tracks present a problem is when you need to go down 8 rows, turn behind the combine in 16 rows, and catch. Other then that it is merely a matter of training the operator to not drive like an idiot cutting donuts. 

The tracks are the only way to go from a flotation standpoint.  Absolutely no comparison to anything else.  Cost is a major issue....you almost have to find them used so that someone else has paid the premium for them.

I don't think 66-43-25's have much  of an application on a grain cart.  They are too short and short on carrying capacity.  A 35.5-32 would be superior I think.  A 73-44-32 or 76-50-32 would have some potential, as would the new Titan radial which is 80" tall by 45" wide or better.  Tall tires offer much more tracklike performance, wide just doesn't cut it very well.