Well, some actual car manufacturers implements sort of steering wheel sens. reduction with speed. That is done for not allowing car to flip or went out of control on speed turns.
I'm happy how car behaves in turns with no aids. But it's getting pretty messy when it trying to, say, change the lane on highspeed. The project I'm working on have pacejka implementation for wheels. I've talked to some experts, they suggest to find wheel's perfectgrip angle (where grip at it's top) and since then, if the speed more then some variable, apply a small amount of steer to wheels.