SAC cards are only valid when there is also waivered airspace in effect specifically for an airshow, waiving the legal minimum aerobatic altitude of 1,500' AGL, among other things. The SAC card itself does not waive any FARs, and doesn't mean you can fly when/where you want at whatever altitude your card is restricted to. The FFI card is no different. It's not a waiver, just an FAA sanctioned statement of formation competency. The min. altitudes stated in the FARs apply to all pilots unless you're in waivered airspace.