On top of what Ron said, there are also safety concerns.
There is a balance between what the loader can hold/lift and tractor stability. If you did something to increase the capacity of the loader significantly, then you run the risk of getting into situations where the rear wheels of the tractor are more likely to come off the ground.
This can be a bad situation, especially when the tractor is moving. It is not always apparent, but the tractor in normal operation is supported by three points. The two rear wheels and the front axle pivot. When one or both rear wheels come off the ground, unless things are perfectly balanced (which is never the case in a practical world), the tractor tends to start leaning towards one side or the other.
So now you have the mass of the loader and tractor moving towards the side...Will it stop when the range of motion of the front axle is reached? Or will it keep going over? Lot of inertia in motion there, including the extra heavy bucket full of whatever.
So along with stressing the tractor, modifying the loader to lift more could also result in increased stressing of the operator as well.
Hope this though is worth something to you... /forums/images/graemlins/smile.gif