A damper does not constitute a dual spring. Dual springs have 2 real live springs in them, and some have 2 real spring + a damper in between. You can't run dual springs on a stock SC head without modification because the spring seats are not wide enough to accept 2 springs.
Stock springs have about 80psi seat pressure. A decent aftermarket single spring will have about 120psi seat pressure. A dual spring worth it's weight will have about 150psi seat pressure.