I've run 140 psi in my Vredestein tires on American Classic 350 Sprint wheels that are only rated for ~120 psi. I didn't have any issues although now that I know better, I won't do it again. The difference for me may be that my tires were actually rated for those pressures. The highest rating I've seen for a 700x28 is 100 psi. I really wouldn't recommend going over that by 20 psi.