I have no idea. I don't even know how a real rally car handbrake behaves. Some other makers such as HE uses a load cell but I think a spring would be enough for me. I don't know if a progressive spring is possible in this case, because you are pulling, not compressing it. I remember the brake mods of the G27 pedals... there was a kind of spring which was more rigid on one of its extremes. So, it got stiffer when bottoming out the pedal. But, as I said, I don't think this can be done with a pulling spring. Anyway, as regard the solution you are trying with the end of the travel, I think anything would be alright and better than a sudden stop like if you were hitting something solid, which would feel wrong.