I ended up using TAROX disks on my fiesta! After upgrading to sierra cosworth 4x4 278mM disks. I managed ro warp the ford ones but the cross drilled and grooved TAROX ones have been fine even with some extended hard drives!

I guess it is "pays your money and take your choice"

The TAROX ones I got were balanced too! which is a bonus in eliminating wheel vibration.