Being too stiff up there at minimum I would expect the front tires to take more of a blow which would distort them and hurt performance. Even if ever so slightly. I would expect the car to be more prone to bounce as well from the front tires, kind of like airing up a basketball too much. Thats an exagerration but illustrates the point. I have never tried running the compression really stiff on the front so I can speak to this only in theory.