0.7mm (1/36th of an inch) is within manufacturing error. considering mustang wheels fit and have practically the same (70.5 vs 70.3 on w-bodies) hub bore as w-bodies, theres nothing to worry about. if you break studs with a 5x114.3 wheel, you either overtighten lugs or have damaged (or worn) studs.
edit: apparently boostengtp managed to break his studs with stock torque stars lol.