Get in touch with Bill Basford for the exact figures.
Higher work rates from the operator being more comfortable and less fatigued whilst maintaining higher speeds (within reason).
Fuel efficiency improved through the front wheels having more constant contact with the ground, than unsuspended machines, increasing overall traction closer to the optimum.
Take it or leave it, but if you have heard Bill talk you will know that he is a very knowledgable and down to earth person.